From 70c4a4a39a10813087441558b876bb22a1771e05 Mon Sep 17 00:00:00 2001
From: Ryan Malloy <ryan@supported.systems>
Date: Sun, 8 Feb 2026 11:29:09 -0700
Subject: [PATCH] test: comprehensive test suite for mcilspy MCP server

Add complete test coverage for the mcilspy package:

- T7: Create TestAssembly.dll fixture with known types/members
- T1: Integration tests using real assembly (metadata reader + ILSpy wrapper)
- T2: MCP tool tests with mocked wrapper for each @mcp.tool()
- T3: Error path tests for regex, file not found, invalid assemblies
- T4: Concurrency tests with asyncio.gather() for parallel operations
- T5: Docstring coverage tests using AST introspection
- T6: Timeout behavior tests for 5-minute subprocess timeout

Test summary:
- 147 tests passing
- 14 skipped (ilspycmd-dependent integration tests)
- 73% code coverage
- All ruff linting checks pass
---
 tests/conftest.py                       |  66 ++-
 tests/fixtures/TestAssembly.cs          | 214 +++++++++
 tests/fixtures/TestAssembly.dll         | Bin 0 -> 8704 bytes
 tests/integration/__init__.py           |   1 +
 tests/integration/test_real_assembly.py | 379 ++++++++++++++++
 tests/test_concurrency.py               | 285 ++++++++++++
 tests/test_docstrings.py                | 301 ++++++++++++
 tests/test_error_paths.py               | 423 +++++++++++++++++
 tests/test_models.py                    |   2 +-
 tests/test_server_tools.py              | 580 ++++++++++++++++++++++++
 tests/test_timeout.py                   | 261 +++++++++++
 11 files changed, 2500 insertions(+), 12 deletions(-)
 create mode 100644 tests/fixtures/TestAssembly.cs
 create mode 100644 tests/fixtures/TestAssembly.dll
 create mode 100644 tests/integration/__init__.py
 create mode 100644 tests/integration/test_real_assembly.py
 create mode 100644 tests/test_concurrency.py
 create mode 100644 tests/test_docstrings.py
 create mode 100644 tests/test_error_paths.py
 create mode 100644 tests/test_server_tools.py
 create mode 100644 tests/test_timeout.py

diff --git a/tests/conftest.py b/tests/conftest.py
index dee9233..78d068d 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -1,33 +1,58 @@
 """Shared pytest fixtures for mcilspy tests."""
 
 import os
+import shutil
 from pathlib import Path
 
 import pytest
 
+# Path to test fixtures directory
+FIXTURES_DIR = Path(__file__).parent / "fixtures"
+
+
+@pytest.fixture
+def test_assembly_path() -> str:
+    """Return path to the custom test assembly.
+
+    This is the primary fixture for tests - uses our custom-built
+    TestAssembly.dll with known types and members.
+    """
+    test_dll = FIXTURES_DIR / "TestAssembly.dll"
+    if not test_dll.exists():
+        pytest.skip("TestAssembly.dll not found - run build_test_assembly.sh first")
+    return str(test_dll)
+
 
 @pytest.fixture
 def sample_assembly_path() -> str:
     """Return path to a .NET assembly for testing.
 
-    Uses a known .NET SDK assembly that should exist on systems with dotnet installed.
+    Falls back to SDK assemblies if test assembly not available.
+    Prefer using test_assembly_path for new tests.
     """
-    # Try to find a .NET SDK assembly
+    # First try our test assembly
+    test_dll = FIXTURES_DIR / "TestAssembly.dll"
+    if test_dll.exists():
+        return str(test_dll)
+
+    # Fallback: Try to find a .NET SDK assembly
     dotnet_base = Path("/usr/share/dotnet/sdk")
     if dotnet_base.exists():
-        # Find any SDK version
         for sdk_dir in dotnet_base.iterdir():
-            test_dll = sdk_dir / "Sdks" / "Microsoft.NET.Sdk" / "tools" / "net10.0" / "Microsoft.NET.Build.Tasks.dll"
-            if test_dll.exists():
-                return str(test_dll)
-            # Try older paths
-            for net_version in ["net9.0", "net8.0", "net7.0", "net6.0"]:
-                test_dll = sdk_dir / "Sdks" / "Microsoft.NET.Sdk" / "tools" / net_version / "Microsoft.NET.Build.Tasks.dll"
+            for net_version in ["net10.0", "net9.0", "net8.0", "net7.0", "net6.0"]:
+                test_dll = (
+                    sdk_dir
+                    / "Sdks"
+                    / "Microsoft.NET.Sdk"
+                    / "tools"
+                    / net_version
+                    / "Microsoft.NET.Build.Tasks.dll"
+                )
                 if test_dll.exists():
                     return str(test_dll)
 
-    # Fallback: any .dll in dotnet directory
-    for root, dirs, files in os.walk("/usr/share/dotnet"):
+    # Last resort: any .dll in dotnet directory
+    for root, _dirs, files in os.walk("/usr/share/dotnet"):
         for f in files:
             if f.endswith(".dll"):
                 return os.path.join(root, f)
@@ -39,3 +64,22 @@ def sample_assembly_path() -> str:
 def nonexistent_path() -> str:
     """Return a path that doesn't exist."""
     return "/nonexistent/path/to/assembly.dll"
+
+
+@pytest.fixture
+def ilspycmd_installed() -> bool:
+    """Check if ilspycmd is available for integration tests."""
+    return shutil.which("ilspycmd") is not None
+
+
+@pytest.fixture
+def skip_without_ilspycmd(ilspycmd_installed):
+    """Skip test if ilspycmd is not installed."""
+    if not ilspycmd_installed:
+        pytest.skip("ilspycmd not installed")
+
+
+@pytest.fixture
+def temp_output_dir(tmp_path):
+    """Provide a temporary directory for test outputs."""
+    return str(tmp_path)
diff --git a/tests/fixtures/TestAssembly.cs b/tests/fixtures/TestAssembly.cs
new file mode 100644
index 0000000..1af8668
--- /dev/null
+++ b/tests/fixtures/TestAssembly.cs
@@ -0,0 +1,214 @@
+using System;
+using System.Threading.Tasks;
+
+namespace TestNamespace
+{
+    /// <summary>
+    /// A test class with various members for testing the mcilspy MCP server.
+    /// </summary>
+    public class TestClass
+    {
+        // Constants for testing string search
+        public const string API_KEY = "test-secret-key";
+        public const string BASE_URL = "https://api.example.com";
+        public const int MAX_RETRIES = 3;
+
+        // Fields
+        public static readonly string BaseUrl = "https://api.example.com";
+        private int _privateField;
+        protected string _protectedField;
+        internal double _internalField;
+
+        // Properties
+        public string Name { get; set; }
+        public int Age { get; private set; }
+        public virtual bool IsActive { get; set; }
+
+        // Events
+        public event EventHandler OnChange;
+        public event EventHandler<string> OnMessage;
+
+        // Constructors
+        public TestClass()
+        {
+            Name = "Default";
+            Age = 0;
+        }
+
+        public TestClass(string name, int age)
+        {
+            Name = name;
+            Age = age;
+        }
+
+        // Methods
+        public void DoSomething()
+        {
+            Console.WriteLine("Hello from DoSomething");
+            OnChange?.Invoke(this, EventArgs.Empty);
+        }
+
+        public string GetGreeting()
+        {
+            return $"Hello, {Name}!";
+        }
+
+        public static int Add(int a, int b)
+        {
+            return a + b;
+        }
+
+        protected virtual void OnPropertyChanged(string propertyName)
+        {
+            OnMessage?.Invoke(this, propertyName);
+        }
+
+        private void PrivateMethod()
+        {
+            _privateField = 42;
+        }
+    }
+
+    /// <summary>
+    /// Interface for testing interface discovery.
+    /// </summary>
+    public interface ITestService
+    {
+        void Execute();
+        Task<string> ExecuteAsync();
+        string ServiceName { get; }
+    }
+
+    /// <summary>
+    /// Another interface for inheritance testing.
+    /// </summary>
+    public interface IConfigurable
+    {
+        void Configure(string settings);
+    }
+
+    /// <summary>
+    /// Struct for testing struct discovery.
+    /// </summary>
+    public struct TestStruct
+    {
+        public int Value;
+        public string Label;
+
+        public TestStruct(int value, string label)
+        {
+            Value = value;
+            Label = label;
+        }
+
+        public override string ToString() => $"{Label}: {Value}";
+    }
+
+    /// <summary>
+    /// Enum for testing enum discovery.
+    /// </summary>
+    public enum TestEnum
+    {
+        None = 0,
+        First = 1,
+        Second = 2,
+        Third = 3
+    }
+
+    /// <summary>
+    /// Delegate for testing delegate discovery.
+    /// </summary>
+    public delegate void TestDelegate(string message);
+
+    /// <summary>
+    /// Delegate with return type.
+    /// </summary>
+    public delegate bool ValidationDelegate<T>(T value);
+
+    /// <summary>
+    /// Service implementation for testing class relationships.
+    /// </summary>
+    public class TestServiceImpl : ITestService, IConfigurable
+    {
+        private string _config;
+
+        public string ServiceName => "TestService";
+
+        public void Execute()
+        {
+            Console.WriteLine($"Executing with config: {_config}");
+        }
+
+        public Task<string> ExecuteAsync()
+        {
+            return Task.FromResult($"Async result from {ServiceName}");
+        }
+
+        public void Configure(string settings)
+        {
+            _config = settings;
+        }
+    }
+
+    /// <summary>
+    /// Nested class for testing nested type discovery.
+    /// </summary>
+    public class OuterClass
+    {
+        public class NestedClass
+        {
+            public string Value { get; set; }
+        }
+
+        private class PrivateNestedClass
+        {
+            public int Secret { get; set; }
+        }
+
+        public NestedClass CreateNested() => new NestedClass();
+    }
+
+    /// <summary>
+    /// Abstract class for testing abstract type discovery.
+    /// </summary>
+    public abstract class AbstractBase
+    {
+        public abstract void AbstractMethod();
+        public virtual void VirtualMethod() { }
+
+        protected string BaseProperty { get; set; }
+    }
+
+    /// <summary>
+    /// Derived class for testing inheritance.
+    /// </summary>
+    public class DerivedClass : AbstractBase
+    {
+        public override void AbstractMethod()
+        {
+            Console.WriteLine("Implemented abstract method");
+        }
+
+        public override void VirtualMethod()
+        {
+            base.VirtualMethod();
+            Console.WriteLine("Overridden virtual method");
+        }
+    }
+}
+
+namespace TestNamespace.SubNamespace
+{
+    /// <summary>
+    /// Class in a sub-namespace for testing namespace filtering.
+    /// </summary>
+    public class SubClass
+    {
+        public const string CONNECTION_STRING = "Server=localhost;Database=test";
+
+        public void SubMethod()
+        {
+            Console.WriteLine("Sub namespace method");
+        }
+    }
+}
diff --git a/tests/fixtures/TestAssembly.dll b/tests/fixtures/TestAssembly.dll
new file mode 100644
index 0000000000000000000000000000000000000000..09c8b53ed1efbd5404a8f93a15d5b151b6929528
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diff --git a/tests/integration/__init__.py b/tests/integration/__init__.py
new file mode 100644
index 0000000..cdf9878
--- /dev/null
+++ b/tests/integration/__init__.py
@@ -0,0 +1 @@
+"""Integration tests that use real ilspycmd calls."""
diff --git a/tests/integration/test_real_assembly.py b/tests/integration/test_real_assembly.py
new file mode 100644
index 0000000..74a8e1d
--- /dev/null
+++ b/tests/integration/test_real_assembly.py
@@ -0,0 +1,379 @@
+"""Integration tests using the custom TestAssembly.dll fixture.
+
+These tests exercise the full stack including ilspycmd calls.
+Tests are skipped if ilspycmd is not installed.
+"""
+
+import pytest
+
+from mcilspy.ilspy_wrapper import ILSpyWrapper
+from mcilspy.metadata_reader import MetadataReader
+from mcilspy.models import (
+    DecompileRequest,
+    EntityType,
+    LanguageVersion,
+    ListTypesRequest,
+)
+
+
+class TestMetadataReaderWithTestAssembly:
+    """Test MetadataReader against our custom test assembly."""
+
+    def test_get_assembly_metadata(self, test_assembly_path):
+        """Test reading metadata from test assembly."""
+        with MetadataReader(test_assembly_path) as reader:
+            meta = reader.get_assembly_metadata()
+
+        assert meta.name == "TestAssemblyProject"
+        assert meta.type_count > 0
+        assert meta.method_count > 0
+
+    def test_list_methods_finds_known_methods(self, test_assembly_path):
+        """Test that we can find methods we know exist."""
+        with MetadataReader(test_assembly_path) as reader:
+            methods = reader.list_methods()
+
+        method_names = [m.name for m in methods]
+
+        # Check for methods we defined in TestClass
+        assert "DoSomething" in method_names
+        assert "GetGreeting" in method_names
+        assert "Add" in method_names
+
+    def test_list_methods_with_type_filter(self, test_assembly_path):
+        """Test filtering methods by type."""
+        with MetadataReader(test_assembly_path) as reader:
+            methods = reader.list_methods(type_filter="TestClass")
+
+        # All methods should be from types containing "TestClass"
+        for method in methods:
+            assert "TestClass" in method.declaring_type
+
+    def test_list_methods_with_namespace_filter(self, test_assembly_path):
+        """Test filtering methods by namespace."""
+        with MetadataReader(test_assembly_path) as reader:
+            methods = reader.list_methods(namespace_filter="SubNamespace")
+
+        # Should only find methods from SubNamespace
+        for method in methods:
+            assert method.namespace is not None
+            assert "SubNamespace" in method.namespace
+
+    def test_list_methods_public_only(self, test_assembly_path):
+        """Test filtering for public methods only."""
+        with MetadataReader(test_assembly_path) as reader:
+            public_methods = reader.list_methods(public_only=True)
+            all_methods = reader.list_methods(public_only=False)
+
+        # Should have fewer public methods than total
+        assert len(public_methods) <= len(all_methods)
+        # All returned methods should be public
+        for method in public_methods:
+            assert method.is_public
+
+    def test_list_fields_finds_known_fields(self, test_assembly_path):
+        """Test that we can find fields we defined."""
+        with MetadataReader(test_assembly_path) as reader:
+            fields = reader.list_fields()
+
+        field_names = [f.name for f in fields]
+
+        # Check for constants and fields we defined
+        assert "API_KEY" in field_names
+        assert "BASE_URL" in field_names
+        assert "MAX_RETRIES" in field_names
+
+    def test_list_fields_constants_only(self, test_assembly_path):
+        """Test filtering for constant fields only."""
+        with MetadataReader(test_assembly_path) as reader:
+            constants = reader.list_fields(constants_only=True)
+
+        # All returned fields should be literals
+        for field in constants:
+            assert field.is_literal
+
+        const_names = [f.name for f in constants]
+        assert "API_KEY" in const_names
+        assert "MAX_RETRIES" in const_names
+
+    def test_list_properties_finds_known_properties(self, test_assembly_path):
+        """Test that we can find properties we defined."""
+        with MetadataReader(test_assembly_path) as reader:
+            properties = reader.list_properties()
+
+        prop_names = [p.name for p in properties]
+
+        # Check for properties we defined
+        assert "Name" in prop_names
+        assert "Age" in prop_names
+        assert "IsActive" in prop_names
+        assert "ServiceName" in prop_names
+
+    def test_list_events_finds_known_events(self, test_assembly_path):
+        """Test that we can find events we defined."""
+        with MetadataReader(test_assembly_path) as reader:
+            events = reader.list_events()
+
+        event_names = [e.name for e in events]
+
+        # Check for events we defined
+        assert "OnChange" in event_names
+        assert "OnMessage" in event_names
+
+    def test_list_resources_empty_for_test_assembly(self, test_assembly_path):
+        """Test that test assembly has no embedded resources."""
+        with MetadataReader(test_assembly_path) as reader:
+            resources = reader.list_resources()
+
+        # Our simple test assembly has no resources
+        assert isinstance(resources, list)
+
+
+class TestILSpyWrapperWithTestAssembly:
+    """Integration tests for ILSpyWrapper using real ilspycmd calls."""
+
+    @pytest.fixture
+    def wrapper(self, skip_without_ilspycmd):
+        """Get wrapper instance, skipping if ilspycmd not available."""
+        return ILSpyWrapper()
+
+    @pytest.mark.asyncio
+    async def test_list_types_finds_classes(self, wrapper, test_assembly_path):
+        """Test listing classes from test assembly."""
+        request = ListTypesRequest(
+            assembly_path=test_assembly_path,
+            entity_types=[EntityType.CLASS],
+        )
+        response = await wrapper.list_types(request)
+
+        assert response.success
+        assert response.total_count > 0
+
+        type_names = [t.name for t in response.types]
+        assert "TestClass" in type_names
+        assert "TestServiceImpl" in type_names
+        assert "OuterClass" in type_names
+
+    @pytest.mark.asyncio
+    async def test_list_types_finds_interfaces(self, wrapper, test_assembly_path):
+        """Test listing interfaces from test assembly."""
+        request = ListTypesRequest(
+            assembly_path=test_assembly_path,
+            entity_types=[EntityType.INTERFACE],
+        )
+        response = await wrapper.list_types(request)
+
+        assert response.success
+
+        type_names = [t.name for t in response.types]
+        assert "ITestService" in type_names
+        assert "IConfigurable" in type_names
+
+    @pytest.mark.asyncio
+    async def test_list_types_finds_structs(self, wrapper, test_assembly_path):
+        """Test listing structs from test assembly."""
+        request = ListTypesRequest(
+            assembly_path=test_assembly_path,
+            entity_types=[EntityType.STRUCT],
+        )
+        response = await wrapper.list_types(request)
+
+        assert response.success
+
+        type_names = [t.name for t in response.types]
+        assert "TestStruct" in type_names
+
+    @pytest.mark.asyncio
+    async def test_list_types_finds_enums(self, wrapper, test_assembly_path):
+        """Test listing enums from test assembly."""
+        request = ListTypesRequest(
+            assembly_path=test_assembly_path,
+            entity_types=[EntityType.ENUM],
+        )
+        response = await wrapper.list_types(request)
+
+        assert response.success
+
+        type_names = [t.name for t in response.types]
+        assert "TestEnum" in type_names
+
+    @pytest.mark.asyncio
+    async def test_list_types_finds_delegates(self, wrapper, test_assembly_path):
+        """Test listing delegates from test assembly."""
+        request = ListTypesRequest(
+            assembly_path=test_assembly_path,
+            entity_types=[EntityType.DELEGATE],
+        )
+        response = await wrapper.list_types(request)
+
+        assert response.success
+
+        type_names = [t.name for t in response.types]
+        assert "TestDelegate" in type_names
+
+    @pytest.mark.asyncio
+    async def test_decompile_specific_type(self, wrapper, test_assembly_path):
+        """Test decompiling a specific type."""
+        request = DecompileRequest(
+            assembly_path=test_assembly_path,
+            type_name="TestNamespace.TestClass",
+            language_version=LanguageVersion.LATEST,
+        )
+        response = await wrapper.decompile(request)
+
+        assert response.success
+        assert response.source_code is not None
+
+        # Check that decompiled code contains expected elements
+        source = response.source_code
+        assert "class TestClass" in source
+        assert "DoSomething" in source
+        assert "GetGreeting" in source
+
+    @pytest.mark.asyncio
+    async def test_decompile_entire_assembly(self, wrapper, test_assembly_path):
+        """Test decompiling the entire assembly."""
+        request = DecompileRequest(
+            assembly_path=test_assembly_path,
+            language_version=LanguageVersion.LATEST,
+        )
+        response = await wrapper.decompile(request)
+
+        assert response.success
+        assert response.source_code is not None
+
+        # Check that all types are present
+        source = response.source_code
+        assert "TestClass" in source
+        assert "ITestService" in source
+        assert "TestStruct" in source
+        assert "TestEnum" in source
+
+    @pytest.mark.asyncio
+    async def test_decompile_to_il(self, wrapper, test_assembly_path):
+        """Test decompiling to IL code."""
+        request = DecompileRequest(
+            assembly_path=test_assembly_path,
+            type_name="TestNamespace.TestClass",
+            show_il_code=True,
+        )
+        response = await wrapper.decompile(request)
+
+        assert response.success
+        assert response.source_code is not None
+
+        # IL code should contain IL-specific keywords
+        source = response.source_code
+        # IL typically shows .method, .field, etc.
+        assert ".class" in source or "IL_" in source
+
+    @pytest.mark.asyncio
+    async def test_decompile_to_output_dir(self, wrapper, test_assembly_path, temp_output_dir):
+        """Test decompiling to an output directory."""
+        request = DecompileRequest(
+            assembly_path=test_assembly_path,
+            output_dir=temp_output_dir,
+        )
+        response = await wrapper.decompile(request)
+
+        assert response.success
+        assert response.output_path is not None
+
+    @pytest.mark.asyncio
+    async def test_decompile_with_project_structure(
+        self, wrapper, test_assembly_path, temp_output_dir
+    ):
+        """Test decompiling with project structure."""
+        request = DecompileRequest(
+            assembly_path=test_assembly_path,
+            output_dir=temp_output_dir,
+            create_project=True,
+        )
+        response = await wrapper.decompile(request)
+
+        assert response.success
+
+    @pytest.mark.asyncio
+    async def test_decompile_nonexistent_type(self, wrapper, test_assembly_path):
+        """Test decompiling a type that doesn't exist."""
+        request = DecompileRequest(
+            assembly_path=test_assembly_path,
+            type_name="NonExistent.FakeClass",
+        )
+        response = await wrapper.decompile(request)
+
+        # Should still succeed but with empty or no matching output
+        # The actual behavior depends on ilspycmd version
+        assert response is not None
+
+
+class TestIntegrationEndToEnd:
+    """End-to-end integration tests covering complete workflows."""
+
+    @pytest.mark.asyncio
+    async def test_discover_and_decompile_workflow(
+        self, skip_without_ilspycmd, test_assembly_path
+    ):
+        """Test the typical workflow: list types, then decompile specific one."""
+        wrapper = ILSpyWrapper()
+
+        # Step 1: List all types
+        list_request = ListTypesRequest(
+            assembly_path=test_assembly_path,
+            entity_types=[EntityType.CLASS],
+        )
+        list_response = await wrapper.list_types(list_request)
+
+        assert list_response.success
+        assert len(list_response.types) > 0
+
+        # Step 2: Find TestServiceImpl
+        service_type = None
+        for t in list_response.types:
+            if t.name == "TestServiceImpl":
+                service_type = t
+                break
+
+        assert service_type is not None
+
+        # Step 3: Decompile it
+        decompile_request = DecompileRequest(
+            assembly_path=test_assembly_path,
+            type_name=service_type.full_name,
+        )
+        decompile_response = await wrapper.decompile(decompile_request)
+
+        assert decompile_response.success
+        assert decompile_response.source_code is not None
+        assert "TestServiceImpl" in decompile_response.source_code
+        assert "ITestService" in decompile_response.source_code
+
+    @pytest.mark.asyncio
+    async def test_metadata_and_decompile_combined(
+        self, skip_without_ilspycmd, test_assembly_path
+    ):
+        """Test using metadata reader and ILSpy wrapper together."""
+        # Use metadata reader for quick discovery
+        with MetadataReader(test_assembly_path) as reader:
+            methods = reader.list_methods(type_filter="TestClass")
+            add_method = None
+            for m in methods:
+                if m.name == "Add":
+                    add_method = m
+                    break
+
+        assert add_method is not None
+        assert add_method.is_static
+
+        # Use ILSpy for decompilation
+        wrapper = ILSpyWrapper()
+        request = DecompileRequest(
+            assembly_path=test_assembly_path,
+            type_name="TestNamespace.TestClass",
+        )
+        response = await wrapper.decompile(request)
+
+        assert response.success
+        # Verify the static method is in the output
+        assert "static" in response.source_code
+        assert "Add" in response.source_code
diff --git a/tests/test_concurrency.py b/tests/test_concurrency.py
new file mode 100644
index 0000000..4052bcb
--- /dev/null
+++ b/tests/test_concurrency.py
@@ -0,0 +1,285 @@
+"""Tests for concurrent tool invocations.
+
+These tests verify that the server handles multiple simultaneous
+tool calls correctly using asyncio.gather().
+"""
+
+import asyncio
+
+import pytest
+
+from mcilspy import server
+from mcilspy.metadata_reader import MetadataReader
+
+
+class TestConcurrentMetadataOperations:
+    """Test concurrent metadata reading operations."""
+
+    @pytest.mark.asyncio
+    async def test_concurrent_search_methods(self, test_assembly_path):
+        """Test multiple search_methods calls running concurrently."""
+        patterns = ["Get", "Do", "Set", "Add", "Create"]
+
+        tasks = [
+            server.search_methods(test_assembly_path, pattern=p) for p in patterns
+        ]
+
+        results = await asyncio.gather(*tasks)
+
+        # All tasks should complete successfully
+        assert len(results) == len(patterns)
+
+        # Each result should be a string
+        for result in results:
+            assert isinstance(result, str)
+
+    @pytest.mark.asyncio
+    async def test_concurrent_search_fields(self, test_assembly_path):
+        """Test multiple search_fields calls running concurrently."""
+        patterns = ["API", "URL", "MAX", "BASE", "VALUE"]
+
+        tasks = [
+            server.search_fields(test_assembly_path, pattern=p) for p in patterns
+        ]
+
+        results = await asyncio.gather(*tasks)
+
+        assert len(results) == len(patterns)
+        for result in results:
+            assert isinstance(result, str)
+
+    @pytest.mark.asyncio
+    async def test_concurrent_search_properties(self, test_assembly_path):
+        """Test multiple search_properties calls running concurrently."""
+        patterns = ["Name", "Value", "Is", "Service"]
+
+        tasks = [
+            server.search_properties(test_assembly_path, pattern=p) for p in patterns
+        ]
+
+        results = await asyncio.gather(*tasks)
+
+        assert len(results) == len(patterns)
+
+    @pytest.mark.asyncio
+    async def test_concurrent_mixed_operations(self, test_assembly_path):
+        """Test different metadata operations running concurrently."""
+        tasks = [
+            server.search_methods(test_assembly_path, pattern="Get"),
+            server.search_fields(test_assembly_path, pattern="API"),
+            server.search_properties(test_assembly_path, pattern="Name"),
+            server.list_events(test_assembly_path),
+            server.list_resources(test_assembly_path),
+            server.get_metadata_summary(test_assembly_path),
+        ]
+
+        results = await asyncio.gather(*tasks)
+
+        assert len(results) == 6
+        for result in results:
+            assert isinstance(result, str)
+            # None of them should have crashed
+            assert "Traceback" not in result
+
+    @pytest.mark.asyncio
+    async def test_concurrent_same_assembly_multiple_readers(self, test_assembly_path):
+        """Test multiple MetadataReaders on the same assembly."""
+        async def read_metadata(path):
+            """Async wrapper for metadata reading."""
+            with MetadataReader(path) as reader:
+                return reader.get_assembly_metadata()
+
+        # Run multiple readers concurrently
+        loop = asyncio.get_event_loop()
+        tasks = [
+            loop.run_in_executor(None, lambda: MetadataReader(test_assembly_path).__enter__().get_assembly_metadata())
+            for _ in range(5)
+        ]
+
+        results = await asyncio.gather(*tasks)
+
+        assert len(results) == 5
+        # All results should have the same assembly name
+        names = [r.name for r in results]
+        assert all(n == names[0] for n in names)
+
+
+class TestConcurrentToolCalls:
+    """Test concurrent MCP tool invocations."""
+
+    @pytest.mark.asyncio
+    async def test_high_concurrency_search(self, test_assembly_path):
+        """Test high number of concurrent searches."""
+        num_concurrent = 20
+
+        tasks = [
+            server.search_methods(test_assembly_path, pattern=f"pattern{i}")
+            for i in range(num_concurrent)
+        ]
+
+        results = await asyncio.gather(*tasks)
+
+        assert len(results) == num_concurrent
+        # Most should return "No methods found" but shouldn't crash
+        for result in results:
+            assert isinstance(result, str)
+
+    @pytest.mark.asyncio
+    async def test_concurrent_with_errors(self, test_assembly_path, nonexistent_path):
+        """Test concurrent calls where some will fail."""
+        tasks = [
+            # These should succeed
+            server.search_methods(test_assembly_path, pattern="Get"),
+            server.search_fields(test_assembly_path, pattern="API"),
+            # These should fail gracefully
+            server.search_methods(nonexistent_path, pattern="test"),
+            server.search_fields(nonexistent_path, pattern="test"),
+        ]
+
+        results = await asyncio.gather(*tasks, return_exceptions=True)
+
+        assert len(results) == 4
+
+        # First two should be successful results
+        assert "GetGreeting" in results[0] or "No methods" in results[0]
+        assert "API_KEY" in results[1] or "No fields" in results[1]
+
+        # Last two should have error messages
+        assert "Error" in results[2]
+        assert "Error" in results[3]
+
+    @pytest.mark.asyncio
+    async def test_concurrent_list_operations(self, test_assembly_path):
+        """Test concurrent list operations."""
+        tasks = [
+            server.list_events(test_assembly_path),
+            server.list_events(test_assembly_path),
+            server.list_resources(test_assembly_path),
+            server.list_resources(test_assembly_path),
+        ]
+
+        results = await asyncio.gather(*tasks)
+
+        assert len(results) == 4
+        # Event results should be identical
+        assert results[0] == results[1]
+        # Resource results should be identical
+        assert results[2] == results[3]
+
+
+class TestConcurrentWithRegex:
+    """Test concurrent operations with regex patterns."""
+
+    @pytest.mark.asyncio
+    async def test_concurrent_regex_searches(self, test_assembly_path):
+        """Test concurrent regex pattern searches."""
+        patterns = [r"^Get.*", r".*Service$", r"On\w+", r".*Base.*"]
+
+        tasks = [
+            server.search_methods(test_assembly_path, pattern=p, use_regex=True)
+            for p in patterns
+        ]
+
+        results = await asyncio.gather(*tasks)
+
+        assert len(results) == 4
+        for result in results:
+            assert isinstance(result, str)
+
+    @pytest.mark.asyncio
+    async def test_concurrent_invalid_regex(self, test_assembly_path):
+        """Test that concurrent invalid regex patterns are handled safely."""
+        patterns = [
+            r"[invalid",  # Invalid
+            r"valid.*",   # Valid
+            r"(?P<broken", # Invalid
+            r"also.*valid", # Valid
+        ]
+
+        tasks = [
+            server.search_methods(test_assembly_path, pattern=p, use_regex=True)
+            for p in patterns
+        ]
+
+        results = await asyncio.gather(*tasks)
+
+        assert len(results) == 4
+        # Invalid patterns should return error messages
+        assert "Invalid regex" in results[0]
+        assert "Invalid regex" in results[2]
+        # Valid patterns should return results (even if empty)
+        assert "Invalid regex" not in results[1]
+        assert "Invalid regex" not in results[3]
+
+
+class TestConcurrentNamespaceFiltering:
+    """Test concurrent operations with namespace filtering."""
+
+    @pytest.mark.asyncio
+    async def test_concurrent_namespace_filtered_searches(self, test_assembly_path):
+        """Test concurrent searches with different namespace filters."""
+        namespace_filters = [
+            "TestNamespace",
+            "SubNamespace",
+            "NonExistent",
+            None,  # No filter
+        ]
+
+        tasks = [
+            server.search_methods(
+                test_assembly_path, pattern="", namespace_filter=ns
+            )
+            for ns in namespace_filters
+        ]
+
+        results = await asyncio.gather(*tasks)
+
+        assert len(results) == 4
+
+
+class TestConcurrencyIsolation:
+    """Test that concurrent operations don't interfere with each other."""
+
+    @pytest.mark.asyncio
+    async def test_results_not_mixed(self, test_assembly_path):
+        """Verify that concurrent operations return their own results."""
+        # Use very specific patterns that should match different things
+        async def search_and_verify(pattern, expected):
+            result = await server.search_methods(test_assembly_path, pattern=pattern)
+            if expected:
+                assert expected in result, f"Expected '{expected}' in result for pattern '{pattern}'"
+            return result
+
+        tasks = [
+            search_and_verify("DoSomething", "DoSomething"),
+            search_and_verify("GetGreeting", "GetGreeting"),
+            search_and_verify("Add", "Add"),
+        ]
+
+        results = await asyncio.gather(*tasks)
+
+        # Verify each result contains only its expected match
+        assert "DoSomething" in results[0]
+        assert "GetGreeting" in results[1]
+        assert "Add" in results[2]
+
+        # Results shouldn't be mixed up
+        assert results[0] != results[1]
+        assert results[1] != results[2]
+
+    @pytest.mark.asyncio
+    async def test_concurrent_metadata_summary_consistent(self, test_assembly_path):
+        """Verify concurrent metadata summary calls return consistent results."""
+        num_concurrent = 10
+
+        tasks = [
+            server.get_metadata_summary(test_assembly_path)
+            for _ in range(num_concurrent)
+        ]
+
+        results = await asyncio.gather(*tasks)
+
+        # All results should be identical
+        first_result = results[0]
+        for result in results[1:]:
+            assert result == first_result, "Concurrent metadata calls returned different results"
diff --git a/tests/test_docstrings.py b/tests/test_docstrings.py
new file mode 100644
index 0000000..4c2e3a7
--- /dev/null
+++ b/tests/test_docstrings.py
@@ -0,0 +1,301 @@
+"""Tests for docstring coverage.
+
+Verifies that all public functions and classes have docstrings.
+Uses AST to introspect the source code.
+"""
+
+import inspect
+
+import pytest
+
+import mcilspy.ilspy_wrapper as wrapper_module
+import mcilspy.metadata_reader as reader_module
+import mcilspy.models as models_module
+
+# Import the modules we want to check
+import mcilspy.server as server_module
+
+
+def get_public_functions_and_classes(module):
+    """Get all public functions and classes from a module.
+
+    Returns a list of (name, obj, has_docstring) tuples.
+    """
+    results = []
+
+    for name in dir(module):
+        if name.startswith("_"):
+            continue
+
+        obj = getattr(module, name)
+
+        # Check if it's a function or class defined in this module
+        if not (inspect.isfunction(obj) or inspect.isclass(obj)):
+            continue
+
+        # Skip imported items
+        if hasattr(obj, "__module__") and obj.__module__ != module.__name__:
+            continue
+
+        has_docstring = bool(inspect.getdoc(obj))
+        results.append((name, obj, has_docstring))
+
+    return results
+
+
+def get_public_methods(cls):
+    """Get all public methods from a class.
+
+    Returns a list of (name, method, has_docstring) tuples.
+    """
+    results = []
+
+    for name, method in inspect.getmembers(cls, predicate=inspect.isfunction):
+        if name.startswith("_") and not name.startswith("__"):
+            continue
+        if name.startswith("__") and name != "__init__":
+            continue
+
+        has_docstring = bool(inspect.getdoc(method))
+        results.append((name, method, has_docstring))
+
+    return results
+
+
+class TestServerModuleDocstrings:
+    """Tests for server.py docstring coverage."""
+
+    def test_all_mcp_tools_have_docstrings(self):
+        """Verify all @mcp.tool() decorated functions have docstrings."""
+        # Find all functions decorated with @mcp.tool()
+        # These are the public API and MUST have docstrings
+        tools = [
+            server_module.check_ilspy_installation,
+            server_module.install_ilspy,
+            server_module.decompile_assembly,
+            server_module.list_types,
+            server_module.generate_diagrammer,
+            server_module.get_assembly_info,
+            server_module.search_types,
+            server_module.search_strings,
+            server_module.search_methods,
+            server_module.search_fields,
+            server_module.search_properties,
+            server_module.list_events,
+            server_module.list_resources,
+            server_module.get_metadata_summary,
+        ]
+
+        missing_docstrings = []
+        for tool in tools:
+            docstring = inspect.getdoc(tool)
+            if not docstring:
+                missing_docstrings.append(tool.__name__)
+
+        assert not missing_docstrings, f"Tools missing docstrings: {missing_docstrings}"
+
+    def test_tool_docstrings_have_args_section(self):
+        """Verify tool docstrings document their arguments."""
+        # Tools with parameters should have Args: section
+        tools_with_params = [
+            server_module.decompile_assembly,
+            server_module.list_types,
+            server_module.generate_diagrammer,
+            server_module.get_assembly_info,
+            server_module.search_types,
+            server_module.search_strings,
+            server_module.search_methods,
+            server_module.search_fields,
+            server_module.search_properties,
+            server_module.list_events,
+            server_module.list_resources,
+            server_module.get_metadata_summary,
+        ]
+
+        missing_args = []
+        for tool in tools_with_params:
+            docstring = inspect.getdoc(tool)
+            sig = inspect.signature(tool)
+
+            # Get non-ctx parameters
+            params = [
+                p
+                for p in sig.parameters.values()
+                if p.name != "ctx" and p.name != "self"
+            ]
+
+            if params and docstring and "Args:" not in docstring:
+                missing_args.append(tool.__name__)
+
+        assert not missing_args, f"Tools missing Args section: {missing_args}"
+
+    def test_helper_functions_have_docstrings(self):
+        """Verify helper functions have docstrings."""
+        helpers = [
+            server_module.get_wrapper,
+            server_module._format_error,
+            server_module._find_ilspycmd_path,
+            server_module._check_dotnet_tools,
+            server_module._detect_platform,
+            server_module._try_install_dotnet_sdk,
+        ]
+
+        missing_docstrings = []
+        for helper in helpers:
+            docstring = inspect.getdoc(helper)
+            if not docstring:
+                missing_docstrings.append(helper.__name__)
+
+        assert not missing_docstrings, f"Helpers missing docstrings: {missing_docstrings}"
+
+
+class TestWrapperModuleDocstrings:
+    """Tests for ilspy_wrapper.py docstring coverage."""
+
+    def test_wrapper_class_has_docstring(self):
+        """Verify ILSpyWrapper class has a docstring."""
+        docstring = inspect.getdoc(wrapper_module.ILSpyWrapper)
+        assert docstring, "ILSpyWrapper class should have a docstring"
+
+    def test_wrapper_public_methods_have_docstrings(self):
+        """Verify ILSpyWrapper public methods have docstrings."""
+        methods_to_check = [
+            "decompile",
+            "list_types",
+            "generate_diagrammer",
+            "get_assembly_info",
+        ]
+
+        missing_docstrings = []
+        for method_name in methods_to_check:
+            method = getattr(wrapper_module.ILSpyWrapper, method_name, None)
+            if method:
+                docstring = inspect.getdoc(method)
+                if not docstring:
+                    missing_docstrings.append(method_name)
+
+        assert not missing_docstrings, (
+            f"ILSpyWrapper methods missing docstrings: {missing_docstrings}"
+        )
+
+
+class TestMetadataReaderDocstrings:
+    """Tests for metadata_reader.py docstring coverage."""
+
+    def test_reader_class_has_docstring(self):
+        """Verify MetadataReader class has a docstring."""
+        docstring = inspect.getdoc(reader_module.MetadataReader)
+        assert docstring, "MetadataReader class should have a docstring"
+
+    def test_reader_public_methods_have_docstrings(self):
+        """Verify MetadataReader public methods have docstrings."""
+        methods_to_check = [
+            "get_assembly_metadata",
+            "list_methods",
+            "list_fields",
+            "list_properties",
+            "list_events",
+            "list_resources",
+        ]
+
+        missing_docstrings = []
+        for method_name in methods_to_check:
+            method = getattr(reader_module.MetadataReader, method_name, None)
+            if method:
+                docstring = inspect.getdoc(method)
+                if not docstring:
+                    missing_docstrings.append(method_name)
+
+        assert not missing_docstrings, (
+            f"MetadataReader methods missing docstrings: {missing_docstrings}"
+        )
+
+
+class TestModelsDocstrings:
+    """Tests for models.py docstring coverage."""
+
+    def test_pydantic_models_have_docstrings(self):
+        """Verify Pydantic model classes have docstrings."""
+        models_to_check = [
+            models_module.DecompileRequest,
+            models_module.DecompileResponse,
+            models_module.ListTypesRequest,
+            models_module.ListTypesResponse,
+            models_module.TypeInfo,
+            models_module.AssemblyInfo,
+        ]
+
+        missing_docstrings = []
+        for model in models_to_check:
+            docstring = inspect.getdoc(model)
+            if not docstring:
+                missing_docstrings.append(model.__name__)
+
+        # Just check that most have docstrings - Pydantic models are self-documenting
+        # through their field names
+        assert len(missing_docstrings) <= 2, (
+            f"Too many models missing docstrings: {missing_docstrings}"
+        )
+
+
+class TestModuleDocstrings:
+    """Tests for module-level docstrings."""
+
+    def test_all_modules_have_docstrings(self):
+        """Verify all mcilspy modules have module-level docstrings."""
+        modules = [
+            server_module,
+            wrapper_module,
+            reader_module,
+            models_module,
+        ]
+
+        missing_docstrings = []
+        for module in modules:
+            if not module.__doc__:
+                missing_docstrings.append(module.__name__)
+
+        # Just warn, don't fail - module docstrings are nice but not critical
+        if missing_docstrings:
+            pytest.skip(f"Modules missing docstrings (non-critical): {missing_docstrings}")
+
+
+class TestDocstringQuality:
+    """Tests for docstring quality (not just presence)."""
+
+    def test_tool_docstrings_not_empty(self):
+        """Verify tool docstrings have meaningful content."""
+        tools = [
+            server_module.decompile_assembly,
+            server_module.list_types,
+            server_module.search_methods,
+        ]
+
+        short_docstrings = []
+        for tool in tools:
+            docstring = inspect.getdoc(tool)
+            if docstring and len(docstring) < 50:
+                short_docstrings.append(f"{tool.__name__}: {len(docstring)} chars")
+
+        assert not short_docstrings, (
+            f"Tools have too-short docstrings: {short_docstrings}"
+        )
+
+    def test_docstrings_describe_purpose(self):
+        """Verify key tool docstrings describe what the tool does."""
+        key_words = {
+            server_module.decompile_assembly: ["decompile", "assembly", "C#"],
+            server_module.list_types: ["types", "list", "class"],
+            server_module.search_methods: ["search", "method"],
+        }
+
+        missing_keywords = []
+        for tool, keywords in key_words.items():
+            docstring = inspect.getdoc(tool).lower() if inspect.getdoc(tool) else ""
+            for keyword in keywords:
+                if keyword.lower() not in docstring:
+                    missing_keywords.append(f"{tool.__name__} missing '{keyword}'")
+
+        assert not missing_keywords, (
+            f"Docstrings missing expected keywords: {missing_keywords}"
+        )
diff --git a/tests/test_error_paths.py b/tests/test_error_paths.py
new file mode 100644
index 0000000..d5a4dd1
--- /dev/null
+++ b/tests/test_error_paths.py
@@ -0,0 +1,423 @@
+"""Tests for error handling paths.
+
+These tests verify that the server handles various error conditions gracefully:
+- Invalid regex patterns
+- ilspycmd not found scenarios
+- Invalid language versions
+- File not found errors
+- Invalid assembly files
+"""
+
+from unittest.mock import AsyncMock, MagicMock, patch
+
+import pytest
+
+from mcilspy import server
+from mcilspy.ilspy_wrapper import ILSpyWrapper
+from mcilspy.metadata_reader import MetadataReader
+from mcilspy.models import EntityType
+
+
+class TestInvalidRegexPatterns:
+    """Tests for invalid regex pattern handling."""
+
+    @pytest.mark.asyncio
+    async def test_search_types_invalid_regex(self, test_assembly_path):
+        """Test search_types with invalid regex pattern."""
+        # Use an invalid regex pattern
+        result = await server.search_types(
+            test_assembly_path,
+            pattern="[invalid(regex",
+            use_regex=True,
+        )
+
+        assert "Invalid regex pattern" in result
+
+    @pytest.mark.asyncio
+    async def test_search_methods_invalid_regex(self, test_assembly_path):
+        """Test search_methods with invalid regex pattern."""
+        result = await server.search_methods(
+            test_assembly_path,
+            pattern="[unclosed",
+            use_regex=True,
+        )
+
+        assert "Invalid regex pattern" in result
+
+    @pytest.mark.asyncio
+    async def test_search_fields_invalid_regex(self, test_assembly_path):
+        """Test search_fields with invalid regex pattern."""
+        result = await server.search_fields(
+            test_assembly_path,
+            pattern="*invalid*",
+            use_regex=True,
+        )
+
+        assert "Invalid regex pattern" in result
+
+    @pytest.mark.asyncio
+    async def test_search_properties_invalid_regex(self, test_assembly_path):
+        """Test search_properties with invalid regex pattern."""
+        result = await server.search_properties(
+            test_assembly_path,
+            pattern="(?P<broken",
+            use_regex=True,
+        )
+
+        assert "Invalid regex pattern" in result
+
+    @pytest.mark.asyncio
+    async def test_search_strings_invalid_regex(self):
+        """Test search_strings with invalid regex pattern."""
+        # Mock the wrapper to avoid needing ilspycmd
+        from mcilspy.models import DecompileResponse
+
+        mock_response = DecompileResponse(
+            success=True,
+            assembly_name="Test",
+            source_code="public class Test { string s = \"hello\"; }",
+        )
+        mock_wrapper = MagicMock()
+        mock_wrapper.decompile = AsyncMock(return_value=mock_response)
+
+        with patch.object(server, "get_wrapper", return_value=mock_wrapper):
+            result = await server.search_strings(
+                "/path/to/test.dll",
+                pattern="[broken",
+                use_regex=True,
+            )
+
+        assert "Invalid regex pattern" in result
+
+
+class TestIlspyCmdNotFound:
+    """Tests for scenarios where ilspycmd is not installed."""
+
+    def test_wrapper_init_raises_when_not_found(self):
+        """Test that ILSpyWrapper raises RuntimeError when ilspycmd not found."""
+        with (
+            patch("shutil.which", return_value=None),
+            patch("os.path.isfile", return_value=False),
+            pytest.raises(RuntimeError) as exc_info,
+        ):
+            ILSpyWrapper()
+
+        assert "ILSpyCmd not found" in str(exc_info.value)
+
+    @pytest.mark.asyncio
+    async def test_decompile_when_not_installed(self):
+        """Test decompile_assembly when ilspycmd is not installed."""
+        with patch.object(
+            server, "get_wrapper", side_effect=RuntimeError("ILSpyCmd not found")
+        ):
+            result = await server.decompile_assembly("/path/to/test.dll")
+
+        assert "Error" in result
+        assert "ILSpyCmd not found" in result
+
+    @pytest.mark.asyncio
+    async def test_list_types_when_not_installed(self):
+        """Test list_types when ilspycmd is not installed."""
+        with patch.object(
+            server, "get_wrapper", side_effect=RuntimeError("ILSpyCmd not found")
+        ):
+            result = await server.list_types("/path/to/test.dll")
+
+        assert "Error" in result
+        assert "ILSpyCmd not found" in result
+
+    @pytest.mark.asyncio
+    async def test_generate_diagrammer_when_not_installed(self):
+        """Test generate_diagrammer when ilspycmd is not installed."""
+        with patch.object(
+            server, "get_wrapper", side_effect=RuntimeError("ILSpyCmd not found")
+        ):
+            result = await server.generate_diagrammer("/path/to/test.dll")
+
+        assert "Error" in result
+
+    @pytest.mark.asyncio
+    async def test_get_assembly_info_when_not_installed(self):
+        """Test get_assembly_info when ilspycmd is not installed."""
+        with patch.object(
+            server, "get_wrapper", side_effect=RuntimeError("ILSpyCmd not found")
+        ):
+            result = await server.get_assembly_info("/path/to/test.dll")
+
+        assert "Error" in result
+
+
+class TestInvalidLanguageVersion:
+    """Tests for invalid language version handling."""
+
+    @pytest.mark.asyncio
+    async def test_decompile_with_invalid_language_version(self):
+        """Test decompile_assembly with invalid language version."""
+        # The LanguageVersion enum should raise ValueError for invalid versions
+        result = await server.decompile_assembly(
+            "/path/to/test.dll",
+            language_version="CSharp99",  # Invalid version
+        )
+
+        # Should return an error about the invalid language version
+        assert "Error" in result
+
+
+class TestFileNotFoundErrors:
+    """Tests for file not found error handling."""
+
+    @pytest.mark.asyncio
+    async def test_search_methods_file_not_found(self, nonexistent_path):
+        """Test search_methods with nonexistent file."""
+        result = await server.search_methods(nonexistent_path, pattern="test")
+
+        assert "Error" in result
+
+    @pytest.mark.asyncio
+    async def test_search_fields_file_not_found(self, nonexistent_path):
+        """Test search_fields with nonexistent file."""
+        result = await server.search_fields(nonexistent_path, pattern="test")
+
+        assert "Error" in result
+
+    @pytest.mark.asyncio
+    async def test_search_properties_file_not_found(self, nonexistent_path):
+        """Test search_properties with nonexistent file."""
+        result = await server.search_properties(nonexistent_path, pattern="test")
+
+        assert "Error" in result
+
+    @pytest.mark.asyncio
+    async def test_list_events_file_not_found(self, nonexistent_path):
+        """Test list_events with nonexistent file."""
+        result = await server.list_events(nonexistent_path)
+
+        assert "Error" in result
+
+    @pytest.mark.asyncio
+    async def test_list_resources_file_not_found(self, nonexistent_path):
+        """Test list_resources with nonexistent file."""
+        result = await server.list_resources(nonexistent_path)
+
+        assert "Error" in result
+
+    @pytest.mark.asyncio
+    async def test_get_metadata_summary_file_not_found(self, nonexistent_path):
+        """Test get_metadata_summary with nonexistent file."""
+        result = await server.get_metadata_summary(nonexistent_path)
+
+        assert "Error" in result
+
+    def test_metadata_reader_file_not_found(self, nonexistent_path):
+        """Test MetadataReader with nonexistent file."""
+        with pytest.raises(FileNotFoundError):
+            MetadataReader(nonexistent_path)
+
+
+class TestInvalidAssemblyFiles:
+    """Tests for handling invalid assembly files."""
+
+    @pytest.fixture
+    def invalid_assembly_path(self, tmp_path):
+        """Create a file that is not a valid .NET assembly."""
+        invalid_file = tmp_path / "invalid.dll"
+        invalid_file.write_text("This is not a valid PE file")
+        return str(invalid_file)
+
+    def test_metadata_reader_invalid_assembly(self, invalid_assembly_path):
+        """Test MetadataReader with an invalid assembly file."""
+        # dnfile may silently fail or raise on invalid assemblies
+        # Either outcome is acceptable - the key is it doesn't crash
+        try:
+            with MetadataReader(invalid_assembly_path) as reader:
+                # If it opens, trying to read should fail or return empty
+                reader.get_assembly_metadata()
+                # If we get here, that's OK - just shouldn't crash
+                assert True
+        except Exception:
+            # An exception is also acceptable for invalid PE files
+            assert True
+
+    @pytest.mark.asyncio
+    async def test_search_methods_invalid_assembly(self, invalid_assembly_path):
+        """Test search_methods with invalid assembly."""
+        result = await server.search_methods(invalid_assembly_path, pattern="test")
+
+        assert "Error" in result
+
+    @pytest.mark.asyncio
+    async def test_get_metadata_summary_invalid_assembly(self, invalid_assembly_path):
+        """Test get_metadata_summary with invalid assembly."""
+        result = await server.get_metadata_summary(invalid_assembly_path)
+
+        assert "Error" in result
+
+
+class TestEntityTypeValidation:
+    """Tests for EntityType enum validation."""
+
+    def test_invalid_entity_type_string(self):
+        """Test EntityType.from_string with invalid type name."""
+        with pytest.raises(ValueError) as exc_info:
+            EntityType.from_string("invalid_type")
+
+        assert "Invalid entity type" in str(exc_info.value)
+
+    def test_invalid_entity_type_single_letter(self):
+        """Test EntityType.from_string with invalid single letter."""
+        with pytest.raises(ValueError) as exc_info:
+            EntityType.from_string("x")
+
+        assert "Invalid entity type" in str(exc_info.value)
+
+    @pytest.mark.asyncio
+    async def test_list_types_with_invalid_entity_type(self):
+        """Test list_types with invalid entity type in list."""
+        # The server should skip invalid entity types with a warning
+        from mcilspy.models import ListTypesResponse
+
+        mock_response = ListTypesResponse(success=True, types=[], total_count=0)
+        mock_wrapper = MagicMock()
+        mock_wrapper.list_types = AsyncMock(return_value=mock_response)
+
+        with patch.object(server, "get_wrapper", return_value=mock_wrapper):
+            # Should not raise, but should skip invalid types
+            result = await server.list_types(
+                "/path/to/test.dll",
+                entity_types=["class", "invalid", "interface"],
+            )
+
+        # Should still work, just skipping the invalid type
+        assert isinstance(result, str)
+
+
+class TestContextInfoFailure:
+    """Tests for handling ctx.info() failures."""
+
+    @pytest.mark.asyncio
+    async def test_decompile_with_failing_context(self):
+        """Test decompile_assembly when ctx.info() fails."""
+        from mcilspy.models import DecompileResponse
+
+        mock_response = DecompileResponse(
+            success=True,
+            assembly_name="Test",
+            source_code="class Test { }",
+        )
+        mock_wrapper = MagicMock()
+        mock_wrapper.decompile = AsyncMock(return_value=mock_response)
+
+        # Create a mock context that fails on info()
+        mock_ctx = MagicMock()
+        mock_ctx.info = AsyncMock(side_effect=Exception("Context info failed"))
+
+        with patch.object(server, "get_wrapper", return_value=mock_wrapper):
+            # The function should handle the failing ctx.info gracefully
+            # Note: Currently ctx is optional and None by default
+            result = await server.decompile_assembly("/path/to/test.dll", ctx=None)
+
+        # Should still succeed since ctx is optional
+        assert "Test" in result
+
+
+class TestEmptyResults:
+    """Tests for handling empty result sets."""
+
+    @pytest.mark.asyncio
+    async def test_search_methods_empty_assembly(self, test_assembly_path):
+        """Test search with pattern that matches nothing."""
+        result = await server.search_methods(
+            test_assembly_path, pattern="ZZZZNONEXISTENT"
+        )
+
+        assert "No methods found" in result
+
+    @pytest.mark.asyncio
+    async def test_search_fields_no_matches(self, test_assembly_path):
+        """Test field search with no matches."""
+        result = await server.search_fields(
+            test_assembly_path, pattern="NONEXISTENT_FIELD_12345"
+        )
+
+        assert "No fields found" in result
+
+    @pytest.mark.asyncio
+    async def test_search_properties_no_matches(self, test_assembly_path):
+        """Test property search with no matches."""
+        result = await server.search_properties(
+            test_assembly_path, pattern="NONEXISTENT_PROPERTY"
+        )
+
+        assert "No properties found" in result
+
+
+class TestInstallIlspy:
+    """Tests for install_ilspy tool error paths."""
+
+    @pytest.mark.asyncio
+    async def test_install_without_dotnet(self):
+        """Test install_ilspy when dotnet is not available."""
+        mock_status = {
+            "dotnet_available": False,
+            "dotnet_version": None,
+            "ilspycmd_available": False,
+            "ilspycmd_version": None,
+            "ilspycmd_path": None,
+        }
+
+        with (
+            patch.object(server, "_check_dotnet_tools", return_value=mock_status),
+            patch.object(
+                server,
+                "_detect_platform",
+                return_value={
+                    "system": "linux",
+                    "distro": "arch",
+                    "package_manager": "pacman",
+                    "install_command": "sudo pacman -S dotnet-sdk",
+                },
+            ),
+        ):
+            result = await server.install_ilspy()
+
+        assert "dotnet CLI is not installed" in result
+
+    @pytest.mark.asyncio
+    async def test_install_already_installed(self):
+        """Test install_ilspy when already installed."""
+        mock_status = {
+            "dotnet_available": True,
+            "dotnet_version": "8.0.100",
+            "ilspycmd_available": True,
+            "ilspycmd_version": "8.2.0",
+            "ilspycmd_path": "/home/user/.dotnet/tools/ilspycmd",
+        }
+
+        with patch.object(server, "_check_dotnet_tools", return_value=mock_status):
+            result = await server.install_ilspy()
+
+        assert "already installed" in result
+
+    @pytest.mark.asyncio
+    async def test_install_fails(self):
+        """Test install_ilspy when installation fails."""
+        mock_status_before = {
+            "dotnet_available": True,
+            "dotnet_version": "8.0.100",
+            "ilspycmd_available": False,
+            "ilspycmd_version": None,
+            "ilspycmd_path": None,
+        }
+
+        # Mock subprocess to simulate installation failure
+        mock_proc = MagicMock()
+        mock_proc.returncode = 1
+        mock_proc.communicate = AsyncMock(return_value=(b"", b"Installation failed"))
+
+        with (
+            patch.object(server, "_check_dotnet_tools", return_value=mock_status_before),
+            patch("asyncio.create_subprocess_exec", return_value=mock_proc),
+        ):
+            result = await server.install_ilspy()
+
+        assert "Installation failed" in result or "failed" in result.lower()
diff --git a/tests/test_models.py b/tests/test_models.py
index 1c30c12..5e8de0d 100644
--- a/tests/test_models.py
+++ b/tests/test_models.py
@@ -3,9 +3,9 @@
 import pytest
 
 from mcilspy.models import (
+    DecompileRequest,
     EntityType,
     LanguageVersion,
-    DecompileRequest,
     ListTypesRequest,
     TypeInfo,
 )
diff --git a/tests/test_server_tools.py b/tests/test_server_tools.py
new file mode 100644
index 0000000..8474de6
--- /dev/null
+++ b/tests/test_server_tools.py
@@ -0,0 +1,580 @@
+"""Tests for MCP server tool functions.
+
+These tests exercise the @mcp.tool() decorated functions in server.py.
+We mock the ILSpyWrapper to test the tool logic independently of ilspycmd.
+"""
+
+from unittest.mock import AsyncMock, MagicMock, patch
+
+import pytest
+
+from mcilspy import server
+from mcilspy.models import (
+    AssemblyInfo,
+    DecompileResponse,
+    ListTypesResponse,
+    TypeInfo,
+)
+
+
+class TestCheckIlspyInstallation:
+    """Tests for check_ilspy_installation tool."""
+
+    @pytest.mark.asyncio
+    async def test_both_installed(self):
+        """Test when both dotnet and ilspycmd are installed."""
+        mock_status = {
+            "dotnet_available": True,
+            "dotnet_version": "8.0.100",
+            "ilspycmd_available": True,
+            "ilspycmd_version": "8.2.0",
+            "ilspycmd_path": "/home/user/.dotnet/tools/ilspycmd",
+        }
+
+        with patch.object(server, "_check_dotnet_tools", return_value=mock_status):
+            result = await server.check_ilspy_installation()
+
+        assert "dotnet CLI" in result
+        assert "8.0.100" in result
+        assert "ilspycmd" in result
+        assert "8.2.0" in result
+        assert "ready to use" in result
+
+    @pytest.mark.asyncio
+    async def test_dotnet_not_installed(self):
+        """Test when dotnet is not installed."""
+        mock_status = {
+            "dotnet_available": False,
+            "dotnet_version": None,
+            "ilspycmd_available": False,
+            "ilspycmd_version": None,
+            "ilspycmd_path": None,
+        }
+
+        with patch.object(server, "_check_dotnet_tools", return_value=mock_status):
+            result = await server.check_ilspy_installation()
+
+        assert "Not found" in result
+        assert "dotnet.microsoft.com" in result
+
+    @pytest.mark.asyncio
+    async def test_ilspycmd_not_installed(self):
+        """Test when dotnet is installed but ilspycmd is not."""
+        mock_status = {
+            "dotnet_available": True,
+            "dotnet_version": "8.0.100",
+            "ilspycmd_available": False,
+            "ilspycmd_version": None,
+            "ilspycmd_path": None,
+        }
+
+        with patch.object(server, "_check_dotnet_tools", return_value=mock_status):
+            result = await server.check_ilspy_installation()
+
+        assert "ilspycmd" in result
+        assert "Not installed" in result
+        assert "install_ilspy" in result.lower() or "dotnet tool install" in result
+
+
+class TestDecompileAssembly:
+    """Tests for decompile_assembly tool."""
+
+    @pytest.mark.asyncio
+    async def test_successful_decompile(self):
+        """Test successful decompilation returns formatted output."""
+        mock_response = DecompileResponse(
+            success=True,
+            assembly_name="TestAssembly",
+            type_name="MyClass",
+            source_code="public class MyClass { }",
+        )
+
+        mock_wrapper = MagicMock()
+        mock_wrapper.decompile = AsyncMock(return_value=mock_response)
+
+        with patch.object(server, "get_wrapper", return_value=mock_wrapper):
+            result = await server.decompile_assembly("/path/to/test.dll")
+
+        assert "Decompilation result" in result
+        assert "TestAssembly" in result
+        assert "public class MyClass" in result
+        assert "```csharp" in result
+
+    @pytest.mark.asyncio
+    async def test_decompile_with_output_dir(self):
+        """Test decompilation to output directory."""
+        mock_response = DecompileResponse(
+            success=True,
+            assembly_name="TestAssembly",
+            output_path="/tmp/output",
+        )
+
+        mock_wrapper = MagicMock()
+        mock_wrapper.decompile = AsyncMock(return_value=mock_response)
+
+        with patch.object(server, "get_wrapper", return_value=mock_wrapper):
+            result = await server.decompile_assembly(
+                "/path/to/test.dll", output_dir="/tmp/output"
+            )
+
+        assert "successful" in result.lower()
+        assert "/tmp/output" in result
+
+    @pytest.mark.asyncio
+    async def test_decompile_failure(self):
+        """Test failed decompilation returns error message."""
+        mock_response = DecompileResponse(
+            success=False,
+            assembly_name="TestAssembly",
+            error_message="Assembly not found",
+        )
+
+        mock_wrapper = MagicMock()
+        mock_wrapper.decompile = AsyncMock(return_value=mock_response)
+
+        with patch.object(server, "get_wrapper", return_value=mock_wrapper):
+            result = await server.decompile_assembly("/path/to/nonexistent.dll")
+
+        assert "failed" in result.lower()
+        assert "Assembly not found" in result
+
+    @pytest.mark.asyncio
+    async def test_decompile_with_type_name(self):
+        """Test decompiling a specific type."""
+        mock_response = DecompileResponse(
+            success=True,
+            assembly_name="TestAssembly",
+            type_name="MyNamespace.MyClass",
+            source_code="namespace MyNamespace { public class MyClass { } }",
+        )
+
+        mock_wrapper = MagicMock()
+        mock_wrapper.decompile = AsyncMock(return_value=mock_response)
+
+        with patch.object(server, "get_wrapper", return_value=mock_wrapper):
+            result = await server.decompile_assembly(
+                "/path/to/test.dll", type_name="MyNamespace.MyClass"
+            )
+
+        assert "MyNamespace.MyClass" in result
+
+    @pytest.mark.asyncio
+    async def test_decompile_exception_handling(self):
+        """Test that exceptions are handled gracefully."""
+        mock_wrapper = MagicMock()
+        mock_wrapper.decompile = AsyncMock(side_effect=RuntimeError("Test error"))
+
+        with patch.object(server, "get_wrapper", return_value=mock_wrapper):
+            result = await server.decompile_assembly("/path/to/test.dll")
+
+        assert "Error" in result
+        assert "Test error" in result
+
+
+class TestListTypes:
+    """Tests for list_types tool."""
+
+    @pytest.mark.asyncio
+    async def test_list_types_success(self):
+        """Test successful type listing."""
+        mock_types = [
+            TypeInfo(name="ClassA", full_name="NS.ClassA", kind="Class", namespace="NS"),
+            TypeInfo(name="ClassB", full_name="NS.ClassB", kind="Class", namespace="NS"),
+            TypeInfo(name="IService", full_name="NS.IService", kind="Interface", namespace="NS"),
+        ]
+        mock_response = ListTypesResponse(
+            success=True,
+            types=mock_types,
+            total_count=3,
+        )
+
+        mock_wrapper = MagicMock()
+        mock_wrapper.list_types = AsyncMock(return_value=mock_response)
+
+        with patch.object(server, "get_wrapper", return_value=mock_wrapper):
+            result = await server.list_types("/path/to/test.dll")
+
+        assert "Types in" in result
+        assert "Found 3 types" in result
+        assert "ClassA" in result
+        assert "ClassB" in result
+        assert "IService" in result
+
+    @pytest.mark.asyncio
+    async def test_list_types_grouped_by_namespace(self):
+        """Test that types are grouped by namespace."""
+        mock_types = [
+            TypeInfo(name="ClassA", full_name="NS1.ClassA", kind="Class", namespace="NS1"),
+            TypeInfo(name="ClassB", full_name="NS2.ClassB", kind="Class", namespace="NS2"),
+        ]
+        mock_response = ListTypesResponse(
+            success=True,
+            types=mock_types,
+            total_count=2,
+        )
+
+        mock_wrapper = MagicMock()
+        mock_wrapper.list_types = AsyncMock(return_value=mock_response)
+
+        with patch.object(server, "get_wrapper", return_value=mock_wrapper):
+            result = await server.list_types("/path/to/test.dll")
+
+        # Should have namespace headers
+        assert "## NS1" in result
+        assert "## NS2" in result
+
+    @pytest.mark.asyncio
+    async def test_list_types_with_entity_types(self):
+        """Test listing specific entity types."""
+        mock_response = ListTypesResponse(
+            success=True,
+            types=[TypeInfo(name="IService", full_name="NS.IService", kind="Interface", namespace="NS")],
+            total_count=1,
+        )
+
+        mock_wrapper = MagicMock()
+        mock_wrapper.list_types = AsyncMock(return_value=mock_response)
+
+        with patch.object(server, "get_wrapper", return_value=mock_wrapper):
+            result = await server.list_types(
+                "/path/to/test.dll", entity_types=["interface"]
+            )
+
+        assert "IService" in result
+        mock_wrapper.list_types.assert_called_once()
+
+    @pytest.mark.asyncio
+    async def test_list_types_no_types_found(self):
+        """Test when no types are found."""
+        mock_response = ListTypesResponse(
+            success=True,
+            types=[],
+            total_count=0,
+            error_message="No types found in assembly",
+        )
+
+        mock_wrapper = MagicMock()
+        mock_wrapper.list_types = AsyncMock(return_value=mock_response)
+
+        with patch.object(server, "get_wrapper", return_value=mock_wrapper):
+            result = await server.list_types("/path/to/test.dll")
+
+        assert "No types found" in result
+
+
+class TestSearchTypes:
+    """Tests for search_types tool."""
+
+    @pytest.mark.asyncio
+    async def test_search_types_finds_matches(self):
+        """Test searching types by pattern."""
+        mock_types = [
+            TypeInfo(name="UserService", full_name="NS.UserService", kind="Class", namespace="NS"),
+            TypeInfo(name="OrderService", full_name="NS.OrderService", kind="Class", namespace="NS"),
+            TypeInfo(name="Helper", full_name="NS.Helper", kind="Class", namespace="NS"),
+        ]
+        mock_response = ListTypesResponse(
+            success=True,
+            types=mock_types,
+            total_count=3,
+        )
+
+        mock_wrapper = MagicMock()
+        mock_wrapper.list_types = AsyncMock(return_value=mock_response)
+
+        with patch.object(server, "get_wrapper", return_value=mock_wrapper):
+            result = await server.search_types("/path/to/test.dll", pattern="Service")
+
+        assert "Search Results" in result
+        assert "UserService" in result
+        assert "OrderService" in result
+        assert "Helper" not in result
+
+    @pytest.mark.asyncio
+    async def test_search_types_case_insensitive(self):
+        """Test case-insensitive search (default)."""
+        mock_types = [
+            TypeInfo(name="SERVICE", full_name="NS.SERVICE", kind="Class", namespace="NS"),
+        ]
+        mock_response = ListTypesResponse(success=True, types=mock_types, total_count=1)
+
+        mock_wrapper = MagicMock()
+        mock_wrapper.list_types = AsyncMock(return_value=mock_response)
+
+        with patch.object(server, "get_wrapper", return_value=mock_wrapper):
+            result = await server.search_types(
+                "/path/to/test.dll", pattern="service", case_sensitive=False
+            )
+
+        assert "SERVICE" in result
+
+    @pytest.mark.asyncio
+    async def test_search_types_with_namespace_filter(self):
+        """Test searching with namespace filter."""
+        mock_types = [
+            TypeInfo(name="ClassA", full_name="App.Services.ClassA", kind="Class", namespace="App.Services"),
+            TypeInfo(name="ClassB", full_name="App.Models.ClassB", kind="Class", namespace="App.Models"),
+        ]
+        mock_response = ListTypesResponse(success=True, types=mock_types, total_count=2)
+
+        mock_wrapper = MagicMock()
+        mock_wrapper.list_types = AsyncMock(return_value=mock_response)
+
+        with patch.object(server, "get_wrapper", return_value=mock_wrapper):
+            result = await server.search_types(
+                "/path/to/test.dll", pattern="Class", namespace_filter="Services"
+            )
+
+        assert "ClassA" in result
+        assert "ClassB" not in result
+
+    @pytest.mark.asyncio
+    async def test_search_types_no_matches(self):
+        """Test when no types match the pattern."""
+        mock_types = [
+            TypeInfo(name="Helper", full_name="NS.Helper", kind="Class", namespace="NS"),
+        ]
+        mock_response = ListTypesResponse(success=True, types=mock_types, total_count=1)
+
+        mock_wrapper = MagicMock()
+        mock_wrapper.list_types = AsyncMock(return_value=mock_response)
+
+        with patch.object(server, "get_wrapper", return_value=mock_wrapper):
+            result = await server.search_types("/path/to/test.dll", pattern="Service")
+
+        assert "No types found" in result
+
+
+class TestSearchMethods:
+    """Tests for search_methods tool (using metadata reader)."""
+
+    @pytest.mark.asyncio
+    async def test_search_methods_uses_metadata_reader(self, test_assembly_path):
+        """Test that search_methods uses MetadataReader directly."""
+        result = await server.search_methods(test_assembly_path, pattern="Do")
+
+        assert "DoSomething" in result
+
+    @pytest.mark.asyncio
+    async def test_search_methods_filters_by_pattern(self, test_assembly_path):
+        """Test method name pattern filtering."""
+        result = await server.search_methods(test_assembly_path, pattern="Get")
+
+        assert "GetGreeting" in result
+        assert "DoSomething" not in result
+
+    @pytest.mark.asyncio
+    async def test_search_methods_public_only(self, test_assembly_path):
+        """Test filtering for public methods."""
+        result = await server.search_methods(
+            test_assembly_path, pattern="Method", public_only=True
+        )
+
+        # Should find public methods
+        assert "Method" in result or "No methods found" in result
+
+
+class TestSearchFields:
+    """Tests for search_fields tool."""
+
+    @pytest.mark.asyncio
+    async def test_search_fields_finds_constants(self, test_assembly_path):
+        """Test finding constant fields."""
+        result = await server.search_fields(test_assembly_path, pattern="API")
+
+        assert "API_KEY" in result
+
+    @pytest.mark.asyncio
+    async def test_search_fields_constants_only(self, test_assembly_path):
+        """Test filtering for constants only."""
+        result = await server.search_fields(
+            test_assembly_path, pattern="", constants_only=True
+        )
+
+        assert "const" in result
+
+
+class TestSearchProperties:
+    """Tests for search_properties tool."""
+
+    @pytest.mark.asyncio
+    async def test_search_properties(self, test_assembly_path):
+        """Test searching for properties."""
+        result = await server.search_properties(test_assembly_path, pattern="Name")
+
+        assert "Name" in result
+
+
+class TestListEvents:
+    """Tests for list_events tool."""
+
+    @pytest.mark.asyncio
+    async def test_list_events(self, test_assembly_path):
+        """Test listing events from assembly."""
+        result = await server.list_events(test_assembly_path)
+
+        assert "OnChange" in result or "No events" in result
+
+
+class TestListResources:
+    """Tests for list_resources tool."""
+
+    @pytest.mark.asyncio
+    async def test_list_resources_empty(self, test_assembly_path):
+        """Test listing resources (test assembly has none)."""
+        result = await server.list_resources(test_assembly_path)
+
+        assert "No embedded resources" in result or "Embedded Resources" in result
+
+
+class TestGetMetadataSummary:
+    """Tests for get_metadata_summary tool."""
+
+    @pytest.mark.asyncio
+    async def test_get_metadata_summary(self, test_assembly_path):
+        """Test getting metadata summary."""
+        result = await server.get_metadata_summary(test_assembly_path)
+
+        assert "Assembly Metadata Summary" in result
+        assert "Name" in result
+        assert "Version" in result
+        assert "Statistics" in result
+        assert "Types" in result
+        assert "Methods" in result
+
+
+class TestGetAssemblyInfo:
+    """Tests for get_assembly_info tool."""
+
+    @pytest.mark.asyncio
+    async def test_get_assembly_info_success(self):
+        """Test getting assembly info successfully."""
+        mock_info = AssemblyInfo(
+            name="TestAssembly",
+            full_name="TestAssembly, Version=1.0.0.0",
+            location="/path/to/test.dll",
+            version="1.0.0.0",
+            target_framework=".NETStandard,Version=v2.0",
+            is_signed=False,
+            has_debug_info=False,
+        )
+
+        mock_wrapper = MagicMock()
+        mock_wrapper.get_assembly_info = AsyncMock(return_value=mock_info)
+
+        with patch.object(server, "get_wrapper", return_value=mock_wrapper):
+            result = await server.get_assembly_info("/path/to/test.dll")
+
+        assert "Assembly Information" in result
+        assert "TestAssembly" in result
+        assert "1.0.0.0" in result
+
+    @pytest.mark.asyncio
+    async def test_get_assembly_info_exception(self):
+        """Test handling of exceptions in get_assembly_info."""
+        mock_wrapper = MagicMock()
+        mock_wrapper.get_assembly_info = AsyncMock(
+            side_effect=FileNotFoundError("File not found")
+        )
+
+        with patch.object(server, "get_wrapper", return_value=mock_wrapper):
+            result = await server.get_assembly_info("/nonexistent/file.dll")
+
+        assert "Error" in result
+
+
+class TestGenerateDiagrammer:
+    """Tests for generate_diagrammer tool."""
+
+    @pytest.mark.asyncio
+    async def test_generate_diagrammer_success(self):
+        """Test successful diagram generation."""
+        mock_response = {
+            "success": True,
+            "output_directory": "/tmp/diagrammer",
+        }
+
+        mock_wrapper = MagicMock()
+        mock_wrapper.generate_diagrammer = AsyncMock(return_value=mock_response)
+
+        with patch.object(server, "get_wrapper", return_value=mock_wrapper):
+            result = await server.generate_diagrammer("/path/to/test.dll")
+
+        assert "successfully" in result.lower()
+        assert "/tmp/diagrammer" in result
+
+    @pytest.mark.asyncio
+    async def test_generate_diagrammer_failure(self):
+        """Test failed diagram generation."""
+        mock_response = {
+            "success": False,
+            "error_message": "Failed to generate diagram",
+        }
+
+        mock_wrapper = MagicMock()
+        mock_wrapper.generate_diagrammer = AsyncMock(return_value=mock_response)
+
+        with patch.object(server, "get_wrapper", return_value=mock_wrapper):
+            result = await server.generate_diagrammer("/path/to/test.dll")
+
+        assert "Failed" in result
+
+
+class TestHelperFunctions:
+    """Tests for helper functions in server.py."""
+
+    def test_format_error_with_context(self):
+        """Test _format_error with context."""
+        error = ValueError("test error")
+        result = server._format_error(error, "testing")
+
+        assert "Error" in result
+        assert "testing" in result
+        assert "test error" in result
+
+    def test_format_error_without_context(self):
+        """Test _format_error without context."""
+        error = RuntimeError("something went wrong")
+        result = server._format_error(error)
+
+        assert "Error" in result
+        assert "something went wrong" in result
+
+    def test_find_ilspycmd_path_not_installed(self):
+        """Test _find_ilspycmd_path when not installed."""
+        with (
+            patch("shutil.which", return_value=None),
+            patch("os.path.isfile", return_value=False),
+        ):
+            result = server._find_ilspycmd_path()
+
+        assert result is None
+
+    def test_find_ilspycmd_path_in_path(self):
+        """Test _find_ilspycmd_path when in PATH."""
+        with patch("shutil.which", return_value="/usr/local/bin/ilspycmd"):
+            result = server._find_ilspycmd_path()
+
+        assert result == "/usr/local/bin/ilspycmd"
+
+    def test_detect_platform_linux(self):
+        """Test platform detection on Linux."""
+        with (
+            patch("platform.system", return_value="Linux"),
+            patch("builtins.open", MagicMock()),
+            patch("shutil.which", return_value="/usr/bin/pacman"),
+        ):
+            result = server._detect_platform()
+
+        assert result["system"] == "linux"
+        assert result["package_manager"] is not None
+
+    def test_detect_platform_windows(self):
+        """Test platform detection on Windows."""
+        with (
+            patch("platform.system", return_value="Windows"),
+            patch("shutil.which", return_value=None),
+        ):
+            result = server._detect_platform()
+
+        assert result["system"] == "windows"
diff --git a/tests/test_timeout.py b/tests/test_timeout.py
new file mode 100644
index 0000000..00c26c1
--- /dev/null
+++ b/tests/test_timeout.py
@@ -0,0 +1,261 @@
+"""Tests for timeout behavior.
+
+Verifies that the 5-minute timeout in ILSpyWrapper works correctly
+and that hanging processes are properly killed.
+"""
+
+import asyncio
+from unittest.mock import AsyncMock, MagicMock, patch
+
+import pytest
+
+from mcilspy.ilspy_wrapper import ILSpyWrapper
+from mcilspy.models import DecompileRequest, LanguageVersion, ListTypesRequest
+
+
+class TestTimeoutBehavior:
+    """Tests for the 5-minute timeout in _run_command."""
+
+    @pytest.fixture
+    def wrapper(self):
+        """Create a wrapper with mocked ilspycmd path."""
+        with patch.object(ILSpyWrapper, "_find_ilspycmd", return_value="/mock/ilspycmd"):
+            return ILSpyWrapper()
+
+    @pytest.mark.asyncio
+    async def test_timeout_returns_error_message(self, wrapper):
+        """Test that timeout produces appropriate error message."""
+        # Create a mock process that never completes
+        mock_process = MagicMock()
+        mock_process.communicate = AsyncMock(side_effect=asyncio.TimeoutError())
+        mock_process.kill = MagicMock()
+        mock_process.wait = AsyncMock()
+
+        with patch("asyncio.create_subprocess_exec", return_value=mock_process):
+            return_code, stdout, stderr = await wrapper._run_command(["test", "args"])
+
+        assert return_code == -1
+        assert "timed out" in stderr.lower()
+        assert "5 minutes" in stderr
+        mock_process.kill.assert_called_once()
+
+    @pytest.mark.asyncio
+    async def test_process_killed_on_timeout(self, wrapper):
+        """Test that the process is killed when timeout occurs."""
+        mock_process = MagicMock()
+        mock_process.communicate = AsyncMock(side_effect=asyncio.TimeoutError())
+        mock_process.kill = MagicMock()
+        mock_process.wait = AsyncMock()
+
+        with patch("asyncio.create_subprocess_exec", return_value=mock_process):
+            await wrapper._run_command(["test"])
+
+        # Verify kill was called
+        mock_process.kill.assert_called_once()
+        # Verify we waited for the process to clean up
+        mock_process.wait.assert_called_once()
+
+    @pytest.mark.asyncio
+    async def test_timeout_in_decompile(self, wrapper, test_assembly_path):
+        """Test timeout behavior during decompile operation."""
+        mock_process = MagicMock()
+        mock_process.communicate = AsyncMock(side_effect=asyncio.TimeoutError())
+        mock_process.kill = MagicMock()
+        mock_process.wait = AsyncMock()
+
+        with patch("asyncio.create_subprocess_exec", return_value=mock_process):
+            request = DecompileRequest(
+                assembly_path=test_assembly_path,
+                language_version=LanguageVersion.LATEST,
+            )
+            response = await wrapper.decompile(request)
+
+        assert response.success is False
+        assert "timed out" in response.error_message.lower()
+
+    @pytest.mark.asyncio
+    async def test_timeout_in_list_types(self, wrapper, test_assembly_path):
+        """Test timeout behavior during list_types operation."""
+        mock_process = MagicMock()
+        mock_process.communicate = AsyncMock(side_effect=asyncio.TimeoutError())
+        mock_process.kill = MagicMock()
+        mock_process.wait = AsyncMock()
+
+        with patch("asyncio.create_subprocess_exec", return_value=mock_process):
+            request = ListTypesRequest(assembly_path=test_assembly_path)
+            response = await wrapper.list_types(request)
+
+        assert response.success is False
+        assert "timed out" in response.error_message.lower()
+
+    @pytest.mark.asyncio
+    async def test_timeout_value_is_5_minutes(self, wrapper):
+        """Verify the timeout value is 300 seconds (5 minutes)."""
+        mock_process = MagicMock()
+        mock_process.communicate = AsyncMock(return_value=(b"output", b""))
+        mock_process.returncode = 0
+
+        with (
+            patch("asyncio.create_subprocess_exec", return_value=mock_process),
+            patch("asyncio.wait_for") as mock_wait_for,
+        ):
+            # Set up the mock to return the communicate result
+            mock_wait_for.return_value = (b"output", b"")
+
+            await wrapper._run_command(["test"])
+
+            # Verify wait_for was called with 300 second timeout
+            mock_wait_for.assert_called_once()
+            args, kwargs = mock_wait_for.call_args
+            assert kwargs.get("timeout") == 300.0 or args[1] == 300.0
+
+
+class TestNormalOperationWithTimeout:
+    """Tests that normal operations complete successfully within timeout."""
+
+    @pytest.fixture
+    def wrapper(self):
+        """Create a wrapper with mocked ilspycmd path."""
+        with patch.object(ILSpyWrapper, "_find_ilspycmd", return_value="/mock/ilspycmd"):
+            return ILSpyWrapper()
+
+    @pytest.mark.asyncio
+    async def test_fast_operation_completes(self, wrapper):
+        """Test that fast operations complete normally."""
+        mock_process = MagicMock()
+        mock_process.communicate = AsyncMock(return_value=(b"success output", b""))
+        mock_process.returncode = 0
+
+        with patch("asyncio.create_subprocess_exec", return_value=mock_process):
+            return_code, stdout, stderr = await wrapper._run_command(["test"])
+
+        assert return_code == 0
+        assert stdout == "success output"
+        assert stderr == ""
+
+    @pytest.mark.asyncio
+    async def test_operation_with_stderr_completes(self, wrapper):
+        """Test that operations with stderr output complete normally."""
+        mock_process = MagicMock()
+        mock_process.communicate = AsyncMock(
+            return_value=(b"output", b"warning message")
+        )
+        mock_process.returncode = 0
+
+        with patch("asyncio.create_subprocess_exec", return_value=mock_process):
+            return_code, stdout, stderr = await wrapper._run_command(["test"])
+
+        assert return_code == 0
+        assert stdout == "output"
+        assert stderr == "warning message"
+
+
+class TestTimeoutWithAsyncioWaitFor:
+    """Tests verifying asyncio.wait_for is used correctly."""
+
+    @pytest.fixture
+    def wrapper(self):
+        """Create a wrapper with mocked ilspycmd path."""
+        with patch.object(ILSpyWrapper, "_find_ilspycmd", return_value="/mock/ilspycmd"):
+            return ILSpyWrapper()
+
+    @pytest.mark.asyncio
+    async def test_wait_for_is_used(self, wrapper):
+        """Verify that asyncio.wait_for is used for timeout."""
+        # Read the source code and verify wait_for is used
+        import inspect
+        source = inspect.getsource(wrapper._run_command)
+        assert "asyncio.wait_for" in source or "wait_for" in source
+
+    @pytest.mark.asyncio
+    async def test_timeout_value_in_source(self, wrapper):
+        """Verify timeout value is 300 seconds in source."""
+        import inspect
+        source = inspect.getsource(wrapper._run_command)
+        # Should have timeout=300.0 or 300 seconds comment
+        assert "300" in source or "5 minute" in source.lower()
+
+
+class TestTimeoutCleanup:
+    """Tests for proper cleanup after timeout."""
+
+    @pytest.fixture
+    def wrapper(self):
+        """Create a wrapper with mocked ilspycmd path."""
+        with patch.object(ILSpyWrapper, "_find_ilspycmd", return_value="/mock/ilspycmd"):
+            return ILSpyWrapper()
+
+    @pytest.mark.asyncio
+    async def test_no_zombie_process_after_timeout(self, wrapper):
+        """Verify process is properly cleaned up after timeout."""
+        mock_process = MagicMock()
+        mock_process.communicate = AsyncMock(side_effect=asyncio.TimeoutError())
+        mock_process.kill = MagicMock()
+        mock_process.wait = AsyncMock()
+        mock_process.returncode = None
+
+        with patch("asyncio.create_subprocess_exec", return_value=mock_process):
+            await wrapper._run_command(["test"])
+
+        # kill() followed by wait() ensures no zombie
+        mock_process.kill.assert_called_once()
+        mock_process.wait.assert_called_once()
+
+    @pytest.mark.asyncio
+    async def test_temp_files_cleaned_after_timeout(self, wrapper, test_assembly_path):
+        """Verify temporary files are cleaned up after timeout."""
+        import os
+        import tempfile
+
+        mock_process = MagicMock()
+        mock_process.communicate = AsyncMock(side_effect=asyncio.TimeoutError())
+        mock_process.kill = MagicMock()
+        mock_process.wait = AsyncMock()
+
+        initial_temp_count = len(os.listdir(tempfile.gettempdir()))
+
+        with patch("asyncio.create_subprocess_exec", return_value=mock_process):
+            request = DecompileRequest(
+                assembly_path=test_assembly_path,
+            )
+            await wrapper.decompile(request)
+
+        # Temp directory should be cleaned up
+        final_temp_count = len(os.listdir(tempfile.gettempdir()))
+        # Should not have more temp files (may have same or fewer)
+        assert final_temp_count <= initial_temp_count + 1  # Allow small margin
+
+
+class TestExceptionHandling:
+    """Tests for exception handling in _run_command."""
+
+    @pytest.fixture
+    def wrapper(self):
+        """Create a wrapper with mocked ilspycmd path."""
+        with patch.object(ILSpyWrapper, "_find_ilspycmd", return_value="/mock/ilspycmd"):
+            return ILSpyWrapper()
+
+    @pytest.mark.asyncio
+    async def test_general_exception_handled(self, wrapper):
+        """Test that general exceptions are caught and returned."""
+        with patch(
+            "asyncio.create_subprocess_exec",
+            side_effect=OSError("Cannot execute"),
+        ):
+            return_code, stdout, stderr = await wrapper._run_command(["test"])
+
+        assert return_code == -1
+        assert stdout == ""
+        assert "Cannot execute" in stderr
+
+    @pytest.mark.asyncio
+    async def test_permission_error_handled(self, wrapper):
+        """Test that permission errors are handled gracefully."""
+        with patch(
+            "asyncio.create_subprocess_exec",
+            side_effect=PermissionError("Access denied"),
+        ):
+            return_code, stdout, stderr = await wrapper._run_command(["test"])
+
+        assert return_code == -1
+        assert "Access denied" in stderr