Improve test detection

[dgarijo]

At the moment, tests will be recognized if:

• Any of the test frameworks we know are used.
• If a class is defined with asserts
• If any defined function has asserts
• If the body has asserts

However, if the test imports another class where the validation is performed, we do not detect it as a test right now. This is not very common, but we should consider it too. Annotated as a TO DO in cli.py (ast_if_test function)