How do you test a guard, interceptor, or pipe in isolation using TestingModule in NestJS?

Question

Accepted Answer

describe('RolesGuard', () => {
  let guard: RolesGuard;
  let reflector: Reflector;

beforeEach(async () => {
    const module = await Test.createTestingModule({
      providers: [RolesGuard, Reflector],
    }).compile();
    guard     = module.get(RolesGuard);
    reflector = module.get(Reflector);
  });

it('allows access when no roles required', () => {
    jest.spyOn(reflector, 'getAllAndOverride').mockReturnValue(undefined);
    const ctx = mockExecutionContext({ user: { roles: [] } });
    expect(guard.canActivate(ctx)).toBe(true);
  });

it('denies access when user lacks required role', () => {
    jest.spyOn(reflector, 'getAllAndOverride').mockReturnValue(['admin']);
    const ctx = mockExecutionContext({ user: { roles: ['user'] } });
    expect(guard.canActivate(ctx)).toBe(false);
  });
});

How do you test a guard, interceptor, or pipe in isolation using TestingModule in NestJS?

Create a mock ExecutionContext manually using a plain object cast to the interface, and pass it directly to the enhancer's method. Use Test.createTestingModule() only to resolve the enhancer with its dependencies. This approach tests the logic in complete isolation from the HTTP stack.

How do you test a guard, interceptor, or pipe in isolation using TestingModule in NestJS?

Create a mock ExecutionContext manually using a plain object cast to the interface, and pass it directly to the enhancer's method. Use Test.createTestingModule() only to resolve the enhancer with its dependencies. This approach tests the logic in complete isolation from the HTTP stack.

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