Testing GraphQL resolvers — unit test services, integration test via executeOperation

Testing resolvers via HTTP requires running a full server, managing ports, and dealing with auth setup. Testing resolvers in isolation misses schema validation and context behavior. Neither extreme is ideal.

Unit test service functions independently. Integration test via Apollo Server's executeOperation which bypasses HTTP.

// Unit test — service function directly
describe('UserService.createUser', () => {
  it('throws when email exists', async () => {
    mockDb.user.findFirst.mockResolvedValue(existingUser);
    await expect(service.createUser({ email: 'x@x.com', name: 'X' })).rejects.toThrow('Email already in use');
  });
});

// Integration test — via executeOperation (no HTTP)
import { ApolloServer } from '@apollo/server';

const server = new ApolloServer({ typeDefs, resolvers });
await server.start();

it('returns user by id', async () => {
  const { body } = await server.executeOperation(
    { query: GET_USER, variables: { id: '1' } },
    { contextValue: { user: mockUser, db: testDb, loaders: createLoaders() } }
  );
  expect(body.kind).toBe('single');
  expect(body.singleResult.data?.user.email).toBe('test@example.com');
});

executeOperation runs the full GraphQL pipeline (parse, validate, execute) without HTTP overhead. Context is injected directly, so auth can be mocked cleanly. It's much faster than supertest HTTP tests.

Writing tests for a GraphQL server with Apollo Server