Add more tests to PyMechanical

[klmcadams]

Add more tests for PyMechanical to increase our coverage when running pytest. This is especially for the embedding tests. Run "pytest -m embedding" to see what coverage is missing. A table will be shown below this coverage line in the terminal:

---------- coverage: platform linux, python x.x.x-final-0 ----------

Ideally, we should have over 80% coverage