Make more flexible two tests in the test_parameters.py file.
Make more flexible two tests in the test_parameters.py file.

Add logic to tests that call the global default_data function so that
they can continue to do that or they can call the new Parameters
default_data classmethod.  Both tests pass regardless of which
default_data they call.

mmessick/Tax-Calculator,mmessick/Tax-Calculator,mcdeaton13/Tax-Calculator,mcdeaton13/Tax-Calculator