Testing if a method returns an Promise

Question

In angularjs, while testing a service, I want to check if the returned object is an Promise.

Right now I am doing the following -

 obj.testMethod()
        .should.be.instanceOf($q.defer());

Answer 1

Testing if an object is a promise is simple:

return !!obj.then && typeof obj.then === 'function';

That's it. If an object has the then method, it's a promise.

It looks like angular's $q doesn't have anything to differentiate it from other kind of promises.