Test promised Microtasks (code)

Once we handle the concepts of the Micro-Macro task we can cover the testing of this environment in practice:

For micro-tasks we can use as an example the following code:

it('Async test sample - plain promise', fakeAsync(() => {
    let test: boolean;

    console.log('Regular synchronous call');

    Promise
        .resolve()
        .then(() => {
            console.log('1st promise called');
            test = true;
            return Promise.resolve();
        })
        .then(() => {
            console.log('2nd promise called');
        });

    console.log('Running test assertions');

    flushMicrotasks();

    expect(test).toBeTruthy(true);
}));

For macro-tasks we can use as an example the following code:

it('Async test example - setTimeout() with flush()', fakeAsync(() => {
    let test = false;

    setTimeout(() => { });

    setTimeout(() => {
        test = true;
        expect(test).toBeTruthy();
    }, 1000);

    flush();
}));

Now we could cover both scenarios, using the micro-macro tasks:

it('Async test example - Promises & setTimeout()', fakeAsync(() => {
    let counter = 0;

    Promise.resolve()
        .then(() => {
            counter += 10;

            setTimeout(() => {
                counter += 1;
            }, 1000);
        });

    expect(counter).toBe(0);

    flushMicrotasks();

    expect(counter).toBe(10);

    tick(500);

    expect(counter).toBe(10);

    tick(500);

    expect(counter).toBe(11);
}));