用Jest模拟测试

Question

I'm using the Flux design pattern in my application and I need to test that an Application Action emits on a given Store in the payload that a component sends.

Using a Dispatcher I send a payload like the following:

dispatcher.dispatch({
  action: ACTION_NAME,
  foo: 'bar',
  emitOn: {
   store: SomeStore, // extends EventEmitter
   componentIds: ['Foo-Bar']
  }
}

The dispatcher is implemented like so (Not necessarily important)

Dispatcher.register((payload) => {
 Actions.call(payload);
 return true;
});

When the dispatcher calls an action the object Actions will call that action and when the action finishes it should call emit on the given store.

My question is how do I test this in my application? I want to know if it's possible to check that emit was called after an action finishes.

To finish an action this function is called Actions.finish(payload)

And if you're curious what finish looks like:

  finish(payload) {
    payload.emitOn.map(emitter => {
      var store = emitter.store;
      emitter.componentIds.map(id => {
        store.emit(id);
      });
    });
  }

My current testing code, but the Error is never thrown:

  jest.mock('./TestStore.js', () => {
    return function() {
      return {
        emit: () => {
          throw new Error('Test Error');
        }
      };
    };
  });

  let ACTION = 'Test-Action';
  let payload = {
    action: ACTION,
    emitOn: [{
      store: TestStore, // The store to emit on
      componentIds: ['Test-Id']
    }]
  };

  expect(() => {
    AppActions.finish(payload);
  }).toThrow(Error);

Answer 1

SO for anyone caring about how to test if a function is called you can spy on a function using jest.spyOn

I found this here Understanding Jest Mocks

I changed my testing code (Much cleaner and the right approach to this kind of testing)

  const emitMock = jest.spyOn(TestStore, 'emit');

  let ACTION = 'Test-Action';
  let payload = {
    action: ACTION,
    emitOn: [{
      store: TestStore, // The store to emit on
      componentIds: ['Test-Id']
    }]
  };

  AppActions.finish(payload);

  expect(emitMock).toHaveBeenCalledTimes(1);