ng-bullet

ng-bullet

Bullet is a library which enhances your unit testing experience with Angular TestBed, greatly increasing execution speed of your tests.

But how does it do that?

Most of the time our angular unit tests for components are configured in the following way:

  beforeEach(async(() => {
        // a really simplified example of TestBed configuration
        TestBed.configureTestingModule({
            declarations: [ /*list of components goes here*/ ],
            imports: [ /* list of providers goes here*/ ]
        })
        .compileComponents();
  }));

This is the common approach of doing that and you will see exactly the same approach while reading Angular documentation or watching Angular courses.

However what it also means is that Angular will re-compile everything we used to configure our TestBed for every test in a suite, thus increasing the overall test execution time.

With ng-bullet the previous code snippet will look like this:

    import { configureTestSuite } from 'ng-bullet';
    ...
    configureTestSuite(() => {
        TestBed.configureTestingModule({
            declarations: [ /*list of components goes here*/ ],
            imports: [ /* list of providers goes here*/ ]
        })
    });

We basically just replaced your code snippet with TestBed configuration on configureTestSuite fucntion call. No need to call compileComponents explicitly. After this ng-bullet will ensure for you that components were compiled only once, still providing all the isolation for your tests and creating new instances of components / services / etc for every test.

ng-bullet also provides 2 handful functions to spin up your component's instances.

createTestContext: <T>(component: Type<T>) => TestCtx<T>;

which creates TestCtx instance for the Angular Component which is not initialized yet (no ngOnInit called). Use case: you can override Component's providers before lifetime hooks were called.

And

createStableTestContext: <T>(component: Type<T>) => Promise<TestCtx<T>>;

which is exactly the same as function above, but this one waits till fixture becomes stable.

Both of them return TestCtx instance which is a wrapper around ComponentFixture, which simplifies your access to some most commonly used features of ComponentFixture.

So don't hesitate and give a try ;)

Performance benefits

The performance gain depends heavily on the number of tests in the suite and the number of components and modules you imported / declared. The more tests you have the bigger will be your benefit. With a really fat configurations it may come close to be N times faster, where N is the number of tests in the suite.

A small comparison from a real project.

This is what it takes to run ~1400 tests completely without using ng-bullet:

And this is how it looks like after most of the suites were updated with ng-bullet usage (there are some suites which are still run on a raw TestBed):

So in this case 300 % speed increase gained.

Installation

npm install ng-bullet or yarn add ng-bullet