When do you use the async function in the TestBed when testing in Angular 2?
When do you use this?
beforeEach(() => { TestBed.configureTestingModule({ declarations: [MyModule], schemas: [NO_ERRORS_SCHEMA], }); });
And when do you use this?
beforeEach(async(() => { TestBed.configureTestingModule({ declarations: [MyModule], schemas: [NO_ERRORS_SCHEMA], }); }));
Can anyone enlighten me on this ?
We wrap our test spec function in another function called async . 2. We place the tests we need to run after the isAuthenticated promise resolves inside this function. This async function executes the code inside its body in a special async test zone. This intercepts and keeps track of all promises created in its body.
tl;dr. In almost all cases, they can be used interchangeably, but using fakeAsync()/tick() combo is preferred unless you need to make an XHR call, in which case you MUST use async()/whenStable() combo, as fakeAsync() does not support XHR calls. For the most part they can be used interchangeably.
Usually, the most convenient way to write async tests is to use async / await . async functions implicitly return a promise. Jasmine will wait until the returned promise is either resolved or rejected before moving on to the next thing in the queue.
async
will not allow the next test to start until the async
finishes all its tasks. What async
does is wrap the callback in a Zone, where all asynchronous tasks (e.g. setTimeout
) are tracked. Once all the asynchronous tasks are complete, then the async
completes.
If you have ever worked with Jasmine outside out Angular, you may have seen done
being passed to the callback
it('..', function(done) { someAsyncAction().then(() => { expect(something).toBe(something); done(); }); });
Here, this is native Jasmine, where we tell Jasmine that this test should delay completion until we call done()
. If we didn't call done()
and instead did this:
it('..', function() { someAsyncAction().then(() => { expect(something).toBe(something); }); });
The test would complete even before the expectation, because the promise resolves after the test is finished executing the synchronous tasks.
With Angular (in a Jasmine environment), Angular will actually call done
behind the scenes when we use async
. It will keep track of all the asynchronous tasks in the Zone, and when they are all finished, done
will be called behind the scenes.
In your particular case with the TestBed
configuration, you would use this generally when you want to compileComponents
. I rarely run into a situation in which I would have to call it otherwise
beforeEach(async(() => { TestBed.configureTestingModule({ declarations: [MyModule], schemas: [NO_ERRORS_SCHEMA], }) .compileComponent().then(() => { fixture = TestBed.createComponent(TestComponent); }); }));
When testing a component that uses templateUrl
(if you are not using webpack), then Angular needs to make an XHR request to get the template, so the compilation of the component would be asynchronous. So we should wait until it resolves before continuing testing.
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