MCP Protocol Compliance Testing Skill
Metadata (Tier 1)
Keywords: testing, protocol, json-rpc, validation, pytest, compliance
File Patterns: **/test_.py, **/tests/.py
Modes: testing_backend
Instructions (Tier 2)
JSON-RPC 2.0 Message Validation
python
import pytest
from pydantic import ValidationError
from server.protocol import JsonRpcRequest, JsonRpcResponse
class TestJsonRpcCompliance:
"""Test JSON-RPC 2.0 protocol compliance."""
def test_valid_request(self):
"""Valid JSON-RPC 2.0 request passes validation."""
request = JsonRpcRequest(
jsonrpc="2.0",
method="tools/call",
params={"name": "search", "arguments": {}},
id=1
)
assert request.jsonrpc == "2.0"
assert request.method == "tools/call"
assert request.id == 1
def test_invalid_jsonrpc_version(self):
"""Invalid jsonrpc version raises ValidationError."""
with pytest.raises(ValidationError) as exc_info:
JsonRpcRequest(
jsonrpc="1.0", # Invalid
method="tools/call",
id=1
)
assert "jsonrpc" in str(exc_info.value).lower()
def test_missing_required_fields(self):
"""Missing required fields raise ValidationError."""
with pytest.raises(ValidationError):
JsonRpcRequest(
jsonrpc="2.0"
# Missing method
)
def test_valid_response(self):
"""Valid JSON-RPC 2.0 response structure."""
response = JsonRpcResponse(
jsonrpc="2.0",
result={"data": "test"},
id=1
)
assert response.result == {"data": "test"}
assert response.error is None
def test_error_response(self):
"""Error response has proper structure."""
error = JsonRpcError(
code=-32601,
message="Method not found",
data={"method": "unknown"}
)
response = JsonRpcResponse(
jsonrpc="2.0",
error=error,
id=1
)
assert response.error.code == -32601
assert response.result is None
Tool Schema Validation
python
from tools.schemas import SearchInput, SearchOutput
class TestToolSchemas:
"""Test Pydantic tool schema compliance."""
def test_valid_input(self):
"""Valid input passes strict mode validation."""
input_data = SearchInput(
query="test",
limit=10,
filter_type="code"
)
assert input_data.query == "test"
assert input_data.limit == 10
def test_strict_mode_prevents_coercion(self):
"""Strict mode blocks type coercion."""
with pytest.raises(ValidationError) as exc_info:
SearchInput(
query="test",
limit="10" # String instead of int
)
# Verify it's a type error, not coercion
assert "int" in str(exc_info.value).lower()
def test_field_constraints(self):
"""Field constraints are enforced (ge, le, etc.)."""
# Below minimum
with pytest.raises(ValidationError):
SearchInput(query="test", limit=0)
# Above maximum
with pytest.raises(ValidationError):
SearchInput(query="test", limit=101)
def test_literal_enum_validation(self):
"""Literal types only accept specified values."""
# Valid literal
input1 = SearchInput(query="test", filter_type="code")
assert input1.filter_type == "code"
# Invalid literal
with pytest.raises(ValidationError):
SearchInput(query="test", filter_type="invalid")
def test_schema_generation(self):
"""Pydantic generates valid JSON Schema."""
schema = SearchInput.model_json_schema()
assert schema["type"] == "object"
assert "query" in schema["properties"]
assert "limit" in schema["properties"]
# Verify constraints in schema
limit_schema = schema["properties"]["limit"]
assert limit_schema["minimum"] == 1
assert limit_schema["maximum"] == 100
def test_output_serialization(self):
"""Output models serialize correctly."""
output = SearchOutput(
results=[{"file": "test.py", "line": 10}],
total_count=1,
execution_time_ms=42
)
dumped = output.model_dump()
assert isinstance(dumped, dict)
assert dumped["total_count"] == 1
Async Tool Execution Tests
python
import pytest
import asyncio
class TestAsyncToolExecution:
"""Test async tool execution patterns."""
@pytest.mark.asyncio
async def test_tool_executes_async(self, mcp_server):
"""Tools execute without blocking."""
result = await mcp_server.call_tool(
"search_code",
{"query": "async def", "limit": 5}
)
assert result is not None
assert "results" in result
@pytest.mark.asyncio
async def test_concurrent_execution(self, mcp_server):
"""Multiple tools execute concurrently."""
start = asyncio.get_event_loop().time()
# Execute concurrently using TaskGroup
async with asyncio.TaskGroup() as tg:
t1 = tg.create_task(
mcp_server.call_tool("search", {"query": "test1"})
)
t2 = tg.create_task(
mcp_server.call_tool("search", {"query": "test2"})
)
duration = asyncio.get_event_loop().time() - start
# Concurrent execution should be faster than sequential
assert duration < 2.0
assert t1.result() is not None
assert t2.result() is not None
@pytest.mark.asyncio
async def test_tool_timeout(self, mcp_server):
"""Tool execution respects timeout."""
with pytest.raises(asyncio.TimeoutError):
await asyncio.wait_for(
mcp_server.call_tool("slow_tool", {}),
timeout=1.0
)
@pytest.mark.asyncio
async def test_tool_cancellation(self, mcp_server):
"""Tool execution can be cancelled."""
task = asyncio.create_task(
mcp_server.call_tool("long_running_tool", {})
)
# Cancel after short delay
await asyncio.sleep(0.1)
task.cancel()
with pytest.raises(asyncio.CancelledError):
await task
Integration Tests
python
class TestMcpIntegration:
"""Full request/response cycle tests."""
@pytest.mark.asyncio
async def test_list_tools(self, mcp_server):
"""list_tools returns valid tool descriptors."""
tools = await mcp_server.list_tools()
assert len(tools) > 0
for tool in tools:
assert "name" in tool
assert "description" in tool
assert "inputSchema" in tool
# Validate schema structure
schema = tool["inputSchema"]
assert schema["type"] == "object"
assert "properties" in schema
@pytest.mark.asyncio
async def test_call_tool_success(self, mcp_server):
"""Successful tool call returns result."""
result = await mcp_server.call_tool(
"search_code",
{"query": "test", "limit": 5}
)
assert "results" in result
assert isinstance(result["results"], list)
@pytest.mark.asyncio
async def test_call_tool_invalid_name(self, mcp_server):
"""Invalid tool name returns error."""
with pytest.raises(ValueError) as exc_info:
await mcp_server.call_tool("nonexistent_tool", {})
assert "unknown" in str(exc_info.value).lower()
@pytest.mark.asyncio
async def test_call_tool_invalid_arguments(self, mcp_server):
"""Invalid arguments raise ValidationError."""
with pytest.raises(ValidationError):
await mcp_server.call_tool(
"search_code",
{"invalid_param": "value"}
)
@pytest.mark.asyncio
async def test_list_resources(self, mcp_server):
"""list_resources returns valid descriptors."""
resources = await mcp_server.list_resources()
for resource in resources:
assert "uri" in resource
assert "name" in resource
assert "mimeType" in resource
# Validate URI scheme
assert resource["uri"].startswith(
("file://", "db://", "api://", "log://")
)
@pytest.mark.asyncio
async def test_read_resource(self, mcp_server):
"""read_resource returns content."""
result = await mcp_server.read_resource(
"file:///project/README.md"
)
assert "contents" in result
assert len(result["contents"]) > 0
content = result["contents"][0]
assert "uri" in content
assert "text" in content or "blob" in content
Error Handling Tests
python
class TestErrorHandling:
"""Test proper error responses."""
@pytest.mark.asyncio
async def test_validation_error_response(self, mcp_server):
"""Validation errors return -32602 (Invalid params)."""
try:
await mcp_server.call_tool(
"search_code",
{"limit": "invalid"} # Type error
)
except McpError as e:
assert e.code == -32602
assert "validation" in e.message.lower()
@pytest.mark.asyncio
async def test_method_not_found_response(self, mcp_server):
"""Unknown methods return -32601 (Method not found)."""
try:
await mcp_server.call_tool("unknown_tool", {})
except McpError as e:
assert e.code == -32601
assert "not found" in e.message.lower()
@pytest.mark.asyncio
async def test_internal_error_response(self, mcp_server):
"""Internal errors return -32603."""
with pytest.raises(McpError) as exc_info:
await mcp_server.call_tool("failing_tool", {})
error = exc_info.value
assert error.code == -32603
Pytest Fixtures
python
# conftest.py
import pytest
from server import create_mcp_server
@pytest.fixture
async def mcp_server():
"""Fixture providing initialized MCP server."""
server = await create_mcp_server("test-server")
yield server
# Cleanup
await server.cleanup()
@pytest.fixture
def sample_search_input():
"""Fixture for valid search input."""
return {
"query": "test query",
"limit": 10,
"filter_type": "code"
}
@pytest.fixture
async def mcp_client():
"""Fixture providing MCP client for integration tests."""
client = McpClient("test-client")
await client.connect()
yield client
await client.disconnect()
Coverage Requirements
bash
# Run tests with coverage pytest --cov=server --cov-report=html --cov-report=term # Coverage targets # - Protocol code (JSON-RPC): 100% # - Tool implementations: 90%+ # - Resource handlers: 90%+ # - Overall: 90%+
Anti-Patterns
❌ Not Testing Strict Mode
python
# WRONG - doesn't verify strict mode prevents coercion
def test_input():
SearchInput(limit="10") # Should fail but test doesn't verify
❌ Missing Async Tests
python
# WRONG - testing async code without pytest-asyncio
def test_async_tool(): # Should be @pytest.mark.asyncio async def
result = call_tool() # Should be await
❌ Not Testing Error Cases
python
# WRONG - only testing happy path
def test_tool():
result = call_tool(valid_input)
assert result # Missing invalid input tests
Resources (Tier 3)
pytest-asyncio: https://pytest-asyncio.readthedocs.io/ Pydantic Testing: https://docs.pydantic.dev/latest/concepts/validation/ JSON-RPC 2.0 Spec: https://www.jsonrpc.org/specification