Create simple API tests to ensure consistency of API

[ziyadedher]

Is your feature request related to a problem? Please describe.
We rely very heavily on mypy to verify that our APIs follow the described contracts; however, given that mypy is not a heavily enforced type-checker and it cannot catch runtime errors such as tensor size mismatches, we should rely on some runtime tests to verify any changes.

Describe the solution you'd like
Use a framework such as pytest with coverage to verify our code is valid. This might involve writing tests for each type of actor/critic/agent and testing them in different environments, but given the modularity of our system, that should not be too difficult to automate.