TST: test_kda.py recommendations

[nawtrey]

This issue was originally opened in GitLab and used to track testing ideas. I've consolidated them into a single list below, but future testing ideas will have their own issues.

Testing ideas:

• Add tests that sum probabilities and check if almost equal to 1
• Check if all generated flux diagrams contain only 1 cycle -- redundant
• For existing tests, add matrix method verification via kda.solve_matrix()
• Add tests that count numbers of partial and directional partial diagrams
• Add test for kda.calculate_pi_difference() to verify the fix for issue kda.calculate_pi_difference(), kda.calculate_thermo_force() are not generating the appropriate functional forms #15
• Add regression test that counts the number of flux diagrams generated for multiple models. This is already halfway implemented, but needs to be expanded to include more known cases
• Add additional unit tests for calculations.calc_thermo_force() (similar to test_thermo_force_4WL) where each test verifies the output of multiple models (4-state, 5-state).
• Add unit tests for calculations.calculate_pi_difference() where each test verifies the output of multiple models (4-state, 4-state with leakage, 5-state)
  Add assertion to test_flux_diagram_counts verifying each flux diagram contains only 1 unique cycle
• Add assertion to test_diagram_counts verifying the list of edges for each partial and directional diagram contains all nodes in the input diagram

[nawtrey]

With #59 merged I checked off the corresponding task.

[nawtrey]

Remaining tasks were addressed in a1e6658. Closing.