A little unittest refactoring
* Add a class decorator to generate tests when using a unittest.TestCase base class
* Add a TestCase subclass with setUp() and tearDown() that sets up
module parameter parsing
* Move test_safe_eval to use the class decorator and ModuleTestCase base
class
* Move testing of set_mode_if_different into its own file and separate
some test methods out so we get better errors and more coverage in
case of errors.
* Naming convention for test cases doesn't need to duplicate information
that's already in the file path.
