blerp | xkcd #1692: Man Page | Video Game library

You should be testing doSomething and doSomethingElse separately with doSomethingElse using a mock of doSomething, with a mocked then methd that can return your value for testing. You basically want to test them separately not at the same time. You're basically coupling doSomething and doSomethingElse in this case which makes testing harder. Testing should be easy, you aren't testing to see if promises work, so use a fake one to move on to testing logic!

I do not find a lack of return value to be an issue myself, there is a return value, you're just chaining it, not storing it.