TestScheduler: Should support *lack* of subscriptions in expectSubscriptions`

[benlesh]

Currently, there is no way to properly test a lack of subscription, AFAICT. (Maybe I'm wrong? haha)

So let's say I want to test something like this:

testScheduler.run(({ cold, expectObservable, expectSubscriptions }) => {
  const source = cold('  ---a---b---c---d---|');
  const expected = '     --------------------';
  const subscriptions = '--------------------';
  const result = source.pipe(subscribeOn(testScheduler, Infinity));
  expectObservable(result).toBe(expected);
  expectSubscriptions(source.subscriptions).toBe(subscriptions);
});

Ran into this while trying to test a bug in subscribeOn.

[cartant]

Can you pass an empty array?

expectSubscriptions(source.subscriptions).toBe([]);

[benlesh]

@cartant ... yes, that's a valid workaround. I think this issue is confusing enough that we should make sure that .toBe(' ') and .toBe('-------') work the same way as .toBe([]).

Further, it's plausible that people will have tests that expect subscriptions like ['^---!', '----', '---^--!'] or the like. I think what we need to do is just take the { subscribed: null, unsubscribed: null } (or whatever that outputs), and filter them out of the resulting arrays. Then everything should "just work" as expected.