Module testing 

Test harness infrastructure for FastMCP.

This module provides utilities for writing comprehensive tests without mocks:

• TestContext: Wrapper around Cx::for_testing() with helper methods
• TestServer: Builder for creating test servers with real handlers
• TestClient: Client for in-process testing with MemoryTransport
• Assertion helpers for validating JSON-RPC and MCP compliance
• Timing utilities for performance measurements
• fixtures: Test data generators for tools, resources, prompts, and messages

Example

use fastmcp_rust::testing::prelude::*;

#[test]
fn test_tool_call() {
    let ctx = TestContext::new();

    // Create a test server with real handlers
    let (router, client_transport, server_transport) = TestServer::builder()
        .build();

    // Create a test client
    let mut client = TestClient::new(client_transport);
    client.initialize().unwrap();

    // Call tool and verify
    let result = client.call_tool("my_tool", json!({"arg": "value"}));
    assert!(result.is_ok());
}

Design Philosophy

• No mocks: All tests use real implementations via MemoryTransport
• Deterministic: Uses asupersync Lab runtime for reproducibility
• Comprehensive logging: Built-in trace support for debugging
• Resource cleanup: Automatic cleanup of spawned tasks

Modules

fixtures

Test fixture generators for FastMCP.

prelude

Prelude for convenient imports in tests.

Structs

MethodTiming

Timing statistics for a method.

Span

A span for tracking nested operations.

Stopwatch

A stopwatch for measuring elapsed time with lap support.

TestClient

Test client for in-process MCP testing.

TestContext

Test context wrapper providing convenient testing utilities.

TestServer

Convenience wrapper for TestServerBuilder.

TestServerBuilder

Builder for creating test servers with real handlers.

TestTrace

Main test trace collector.

TestTraceBuilder

Builder for creating test traces.

TestTraceOutput

Complete trace of a test execution.

Timer

A simple timer that fires after a duration.

TimingStats

Timing statistics for a set of measurements.

TraceRetentionConfig

Configuration for trace file cleanup.

TraceSummary

Summary statistics for a trace.

Enums

TraceEntry

Entry type in a trace.

TraceLevel

Log level for trace entries.

Functions

assert_content_valid

Validates that content is MCP-compliant.

assert_is_notification

Validates that a JSON-RPC request is a valid notification.

assert_is_request

Validates that a JSON-RPC request is a valid request (not notification).

assert_json_rpc_error

Validates that a JSON-RPC response indicates an error.

assert_json_rpc_success

Validates that a JSON-RPC response indicates success.

assert_json_rpc_valid

Validates that a JSON-RPC message is well-formed.

assert_mcp_compliant

Validates that an MCP response is compliant with the protocol.

assert_prompt_valid

Validates that a prompt definition is MCP-compliant.

assert_resource_valid

Validates that a resource definition is MCP-compliant.

assert_tool_valid

Validates that a tool definition is MCP-compliant.

cleanup_old_traces

Cleans up old trace files based on retention configuration.

get_trace_dir

Returns the trace output directory from FASTMCP_TEST_TRACE_DIR or defaults to “test_traces”.

is_trace_enabled

Check if test tracing is enabled via environment variable.

measure_duration

Measures the duration of a closure execution.