Simple way to unit test classes whose collaborators return promises

[tomdcc]

Handlers calling collaborator classes who return promises need those promises to have been created using the same ExecController that the handler is run with. This is a bit of a pain when running with UnitTest.handle.

FWIW for my purposes it was enough to write a utility method to grab it from the stored threadlocal:

static <T> Promise<T> instaPromise(T val) {
    ExecController.current().get().control.promise { f -> f.success(val) }
}

[ldaley]

This was effectively solved by the new ExecController.execController() method which lazily binds to the exec controller.

So, you can now do ExecController.execController().promiseOf(val). I think we can sweeten this even more by some static methods on Promise, but that can be a separate thing.