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:
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:
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.
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.
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
So don't hesitate and give a try ;)
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
So in this case 300 % speed increase gained.
npm install ng-bullet or
yarn add ng-bullet