These are actually synonymous -- getFormFactory() will create a form factory instance internally. The old code is actually more performant than your change. The reason no unit tests fail currently is because we actually have a test that verifies that the form element manager is identical in the two objects.

Can you indicate why you would want to alter this? A unit test detailing the use case would make the most sense, as right now, I'm unclear what the purpose of the change is.