Nathan Cooper Nathan Cooper - 3 months ago 12
TypeScript Question

How to test a method returning a Promise

I'm writing an Angular 2 RC5 application, and unit testing using Karma and Jasmine.

I have a method that returns a

Promise<Foo>
(It's on top of a call to angular's http.post) I want to run some assertions after that finishes.

Something like this doesn't work

let result = myService.getFoo();
result.then(rslt => expect(1+1).toBe(3)); // the error is lost


This creates an 'Unhandled Promise rejection' warning, but the error is suppressed and the test passes. How do I run assertions based on my resolved promise?

Notes:


  • The .catch() method doesn't seem to be what I'm after. I don't want to log or do anything that continues normal program flow, I want to fail the test.

  • I've seen code that looks like
    $rootScope.$digest();
    . I'm not sure what the typescript equivalent of this sort of thing is. There doesn't seem to be a way of saying: "I have a promise, I'm going to wait here until I have a synchronous result".


Answer

The test should look something like this:

it('should getFoo', function (done) {
  let result = myService.getFoo();
  result
    .then(rslt => expect(rslt).toBe('foo'))
    .then(done);
});