api-testing

Overview

Tests target handler behavior directly — call handler(input, ctx), assert on the return value or thrown error. The framework's handler factory (try/catch, formatting, telemetry) is not involved. Use createMockContext from @cyanheads/mcp-ts-core/testing to construct the ctx argument.

Additional exports from /testing: createMockSession() binds a mock handler context to an HTTP session; createFetchMock() provides a strict upstream HTTP fake; runToolContract() executes a definition through schema, handler, formatting, enrichment/content, and production-shaped error-envelope checks. createMockLogger() returns a standalone MockContextLogger, and createInMemoryStorage(options?) provides a real StorageService backed by InMemoryProvider.

Philosophy: Test behavior, not implementation. Refactors should not break tests. Match the repo's existing test layout: fresh scaffolds use tests/, while colocated src/**/*.test.ts files are also supported. Integration tests at I/O boundaries over unit tests of internals.

mcpTest — fixture-based Vitest test

mcpTest is a test.extend-based Vitest test that provides ctx, session, fetchMock, and storage as per-test fixtures — fresh instances for every test, eliminating boilerplate and enforcing isolation automatically. fetchMock is installed as globalThis.fetch only when requested by a test and restored afterward.

import { mcpTest } from '@cyanheads/mcp-ts-core/testing/vitest';

mcpTest('echoes the message', async ({ ctx }) => {
  const result = await echoTool.handler(echoTool.input.parse({ message: 'hi' }), ctx);
  expect(result.message).toBe('hi');
});

mcpTest('uses storage fixture', async ({ ctx, storage }) => {
  const svc = new MyService(config, storage);
  const result = await svc.doWork(ctx);
  expect(result).toBeDefined();
});

mcpTest('stubs an upstream HTTP boundary', async ({ fetchMock }) => {
  fetchMock.route({
    match: 'https://api.example.test/items/42',
    respond: Response.json({ id: '42' }),
  });
  await expect(loadItem('42')).resolves.toMatchObject({ id: '42' });
});