mcp-arduino/TESTING_FIXES_SUMMARY.md

FastMCP Testing Fixes Summary

Issues Found and Fixed

1. Arduino Sketch Tests (test_arduino_sketch.py)

Issue: The create_sketch method calls _open_file() which opens sketch files in text editor during test runs.

Fixed:

• Added with patch.object(sketch_component, '_open_file'): to test_create_sketch_already_exists
• Pattern: Mock _open_file method to prevent file opening during tests

Status: ✅ FIXED - All Arduino sketch tests now pass

2. Integration Tests (test_integration.py)

Issues:

• Incorrect FastMCP resource access pattern: Used .content instead of .read()
• Incorrect FastMCP tool invocation pattern: Used .invoke() instead of .run(arguments_dict)
• Attempted to access mcp_server.app.sketch_component which doesn't exist
• Tools require active FastMCP context to run, causing "No active context found" errors

Partially Fixed:

• ✅ Resource access: Changed from resource.content to await resource.read()
• ✅ Tool invocation method: Changed from tool.invoke() to tool.run({})
• ❌ Context issues: Tools still need proper FastMCP context management
• ❌ Component access: Tests try to access non-existent mcp_server.app attribute

Status: 🟡 PARTIALLY FIXED - 10/18 tests pass, 8 still fail due to context issues

Proper FastMCP Testing Patterns

Resource Access Pattern

# ❌ Incorrect
resource = await mcp_server.get_resource("uri")
content = resource.content

# ✅ Correct
resource = await mcp_server.get_resource("uri")
content = await resource.read()

Tool Invocation Pattern

# ❌ Incorrect
tool = await mcp_server.get_tool("tool_name")
result = await tool.invoke(param1="value1")

# ✅ Correct
tool = await mcp_server.get_tool("tool_name")
result = await tool.run({"param1": "value1"})

Component Method Mocking

# ❌ Incorrect (for integration tests)
with patch.object(mcp_server.app.sketch_component, '_open_file'):

# ✅ Correct (for component tests)
with patch.object(sketch_component, '_open_file'):

Recommended Next Steps

Option 1: Use FastMCP Testing Utilities

Rewrite integration tests to use run_server_in_process from fastmcp.utilities.tests:

from fastmcp.utilities.tests import run_server_in_process

def test_server_integration():
    with run_server_in_process(create_server, config) as server_url:
        # Make HTTP/MCP requests to server_url
        # This provides proper context management

Option 2: Simplify Integration Tests

Focus integration tests on:

• Server creation and component registration
• Tool/resource metadata validation
• Resource content validation (without execution)
• Error handling for invalid configurations

Remove complex workflow tests that require tool execution with context.

Option 3: Use Component-Level Testing

Move detailed functionality tests to component-level tests where proper mocking can be applied:

• test_arduino_sketch.py - ✅ Already working
• test_arduino_library.py
• test_arduino_board.py
• etc.

Files Modified

/home/rpm/claude/mcp-arduino-server/tests/test_arduino_sketch.py

• Added _open_file mocking to test_create_sketch_already_exists
• All tests now pass ✅

/home/rpm/claude/mcp-arduino-server/tests/test_integration.py

• Fixed resource access patterns (10 tests now pass)
• Fixed tool invocation method signatures
• Updated error condition assertions
• 8 tests still failing due to context management issues

Security & Best Practices Applied

1. File Opening Prevention: All _open_file calls are mocked to prevent opening text editors during tests
2. Subprocess Mocking: Arduino CLI calls are properly mocked with patch('subprocess.run')
3. Error Handling: Tests properly handle error conditions (missing arduino-cli, etc.)
4. Isolation: Tests use temporary directories and proper cleanup

FastMCP Architecture Compliance

The fixes follow proper FastMCP patterns:

• Resources use .read() method for content access
• Tools use .run(arguments_dict) method for execution
• Components are tested in isolation with proper mocking
• Integration tests focus on metadata and registration, not execution