Add some failing n=5 tests.
Rewrite previous contains2 tests to use gets function.
Refactor to create _contains, that gives reasons for failure.  Add tests for _contains.
In testing discover ThisCannotHappen bug.
Fix bug should be mass_1 - mass_2, not vice versa.  It's a BLUNDER.
Find bug in _helper, which might explain bad output.
Resolve bug in helper, which fixes known bad output. It's a BLUNDER.
Change expected output for compute.pya nd constants.py.  Should have been part of previous commit.
For #2 add tests that should succeed - we're missing an expected contribution.
Change code to give correct values for n = 5, and adjust tests to suit.