2-9 Isolate the component from the world using HTTP interceptor

⚪ ️2.9 Isolate the component from the world using HTTP interceptor §

:white_check_mark: Do: Isolate the component under test by intercepting any outgoing HTTP request and providing the desired response so the collaborator HTTP API won’t get hit. Nock is a great tool for this mission as it provides a convenient syntax for defining external services behavior. Isolation is a must to prevent noise and slow performance but mostly to simulate various scenarios and responses - A good flight simulator is not about painting clear blue sky rather bringing safe storms and chaos. This is reinforced in a Microservice architecture where the focus should always be on a single component without involving the rest of the world. Though it’s possible to simulate external service behavior using test doubles (mocking), it’s preferable not to touch the deployed code and act on the network level to keep the tests pure black-box. The downside of isolation is not detecting when the collaborator component changes and not realizing misunderstandings between the two services - Make sure to compensate for this using a few contract or E2E tests

❌ Otherwise: Some services provide a fake version that can be deployed by the caller locally, usually using Docker - This will ease the setup and boost the performance but won’t help with simulating various responses; Some services provide ‘sandbox’ environment, so the real service is hit but no costs or side effects are triggered - This will cut down the noise of setting up the 3rd party service but also won’t allow simulating scenarios

✏ Code Examples

:clap: Preventing network calls to externous components allows simulating scenarios and minimizing the noise §

// Intercept requests for 3rd party APIs and return a predefined response 
beforeEach(() => {
  nock('http://localhost/user/').get(`/1`).reply(200, {
    id: 1,
    name: 'John',
  });
});