Add basic unit tests for pipelines.py

[ejseqera]

Will serve as a starting point for additional unit tests for other classes, and run with CI/CD

• Can use the monkeypatch fixture to make the tests simpler

[ejseqera]

I've started implementing tests on the linked development branch.

Starting with pipelines.py, my intention is to test in the following way:

1. Mocking tests (in tests/unit):

• Mock the _tw_run method through isolation of methods in Pipelines() (i.e. Pipelines.add(), and Pipelines.get_list()) and making sure these correctly call the _tw_run method with correct arguments (this is the lowest level of isolation for testing)
• Mock subprocess to make sure methods in Pipelines() work when arguments are passed to _tw_run and a shell command string is correctly called/constructed (do the commands match with how you would run it on the CLI?)

2. Integration tests (in tests/integration):

• Test methods through actual execution of the subprocess commands in a suitable environment
• For example, on scidev/testing or scidev/showcase, include a test that will actually run Pipelines.get_list("scidev/testing")
• Here, we can make assertions about the JSON outputs and etc
• Long term, this should include a workspace like scidev/showcase that is reliably maintained but how do we set up an access token to use in a different environment (i.e. CI/CD)?
• These don't have to be immediate because if we have tests that mock subprocess we have assurance we're constructing the correct CLI commands as mentioned above

[ejseqera]

Need to update these based on the new implementation of the wrapper.