Move function case to its own test
Separate class and class with namespace tests
Combine and rename tests for nonexistent targets
Add some more cases for nonexistent targets
Refactor resolveCoversToReflectionObjects() to a few top-level blocks

Early returns avoid deep nesting and allow one branch for each of five
cases:
 - Global function
 - Entire class and its ancestors
 - Entire class
 - Methods of a certain visibility
 - Method of a class