Testing a function in Angular2 that triggers an HTTP service

I am currently facing a challenge while attempting to test a function that invokes an HTTP request service and then performs actions in the subscribe section (calls another function and sets a variable). Initially, I tried calling the function directly assuming that the request service would be triggered automatically, leading to the execution of the subscribe section. However, it seems this approach is not yielding the expected results.

The specific function I intend to test is as follows:

  public trainBot() {
    this.isTraining = true;
    this.requestsService.trainModel(this.botId, false)
      .subscribe(response => {
        this.trainingStatus = this.trainingStatusMapping[response['status']];
        this.pollTrainingStatus();
      });
  }

This is what my current test looks like (but it is not functioning as desired).

it('should poll the training status', () => {
    spyOn(component, 'pollTrainingStatus').and.callThrough();
    component.trainBot();
    fixture.detectChanges();
    expect(component.pollTrainingStatus).toHaveBeenCalled();
  });

Therefore, I am seeking guidance on how to effectively test the portion inside the .subscribe(...) block.

Update:

Following a suggestion, I have updated my test with returnValue and async but unfortunately, it is still not producing the expected output. Here is the revised version:

it('should poll the training status', fakeAsync(() => {
    component.trainBot();
    spyOn(service, 'trainModel').and.returnValue(Observable.of({'status': 'training'}));
    spyOn(component, 'pollTrainingStatus').and.callThrough();
    fixture.detectChanges();
    tick(1);
    expect(service.trainModel).toHaveBeenCalled();
    expect(component.pollTrainingStatus).toHaveBeenCalled();
  }));

Despite these changes, the error remains consistent.

Answer №1

Before running the trainBot() method, make sure to create your Spies. This will help in fixing the tests.

it('should check the training status', () => {
  spyOn(service, 'trainModel').and.returnValue(Observable.of({'status': 'training'}));
  spyOn(component, 'pollTrainingStatus');

  component.trainBot();

  expect(service.trainModel).toHaveBeenCalled();
  expect(component.pollTrainingStatus).toHaveBeenCalled();
}));

When it comes to testing strategies, focus on testing the component rather than the service. Avoid letting the service method call through in your tests.

spyOn(service, 'trainModel').and.returnValue(Observable.of({'status': 'training'}));

Furthermore, aim to test the smallest unit possible in a unit test. Instead of testing the callback directly in this test, consider creating a named method for the callback and verify its functionality in separate tests.

public trainBot() {
  this.isTraining = true;
  this.requestsService.trainModel(this.botId, false)
      .subscribe(response => this.onTrainbotSuccess(response));
}

public onTrainbotSuccess(response) {
  this.trainingStatus = this.trainingStatusMapping[response['status']];
  this.pollTrainingStatus();
}

In this scenario, you can test if the response method is being executed.

it('should invoke service.trainModel', () => {
  spyOn(service, 'trainModel').and.returnValue(Observable.of({'status': 'training'}));

  component.trainBot();

  expect(service.trainModel).toHaveBeenCalled();
});

it('should trigger onTrainbotSuccess() with success responses', () => {
  spyOn(component, 'onTrainbotSuccess');
  spyOn(service, 'trainModel').and.returnValue(Observable.of({'status': 'training'}));

  component.trainBot();

  expect(component.onTrainbotSuccess).toHaveBeenCalled();
});

Finally, write tests specifically for the actions performed in the success callback.

it('should check the training status', () => {
  spyOn(component, 'pollTrainingStatus');

  component.onTrainbotSuccess({'status': 'training'});

  expect(component.pollTrainingStatus).toHaveBeenCalled();
});

Answer №2

The subscribe() function executes asynchronously, causing your assertion to run before this.pollTrainingStatus() is called. To address this, you should utilize either the async() or fakeAsync() utility functions. Check out the official Angular documentation for more information: async() or fakeAsync().

If you opt for using fakeAsync(), your code snippet may resemble the following:

import { fakeAsync } from '@angular/core/testing';

it('should poll the training status', fakeAsync(() => {
  ...
  expect(component.pollTrainingStatus).toHaveBeenCalled();
}));

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