Install requires pytest, new invariant property tests, and a bug-fix

• Including pytest in the installation requirements. Technically, any test runner can be used but with all base package assumptions being built around pytest this feels like the right assumption to call out as an install dependency. It is the default behavior.
• Updated controller for test file exclusion to explicitly match prefix or suffix cases for "test_" and "_test" per pytest conventions.
• Changed error and unknown status results to console color as yellow instead of red.
• Added multiple invariant property tests, primarily to controller and cache.
• Added hypothesis to the test components of extras_require.
• Moved to @property decorators for internal class properties that should only be set at initialization, may add custom setters at a later time.
• Fixed a zero-division bug in the cli when reporting coverage percentage.