Jasmine: Expecting Error to be Thrown in a Async Function

Question

I have an async function in my angular2 app for which I want to write a unit test. Imagine my function is like this:

myFunc(a: int): Promise<void> {
    if (a == 1)
        throw new Error('a should not be 1');

    let body = {
        value: a
    };
    return apiService.patch('/url/', JSON.stringify(body)).toPromise();
}

Now, I'm thinking of checking that if condition. I tried the following code; but, this test always fails since my code actually does not wait for any results:

it('should throw error if a = 1', () => {
    expect(() => {
        mySerivce.myFunc(1);
    }).toThrow(new Error('a should not be 1'));
})

I don't know how I should write unit tests for these types of logics...

Answer 1

Nowadays jasmine (3.3+) supports this natively:

https://jasmine.github.io/api/3.4/async-matchers.html

it('should...', async () => {
  await expectAsync(myService.myFunc(1))
    .toBeRejectedWith(new Error('a should not be 1'));
});