Update tests to work with setuptools >= 72

[BenjaminRodenberg]

Support for the test command has been removed in Setuptools 72. Currently, our (mock) tests require this command. We, therefore, need to update our tests to make them futureproof.

[BenjaminRodenberg]

I'm restricting to setuiptools<72 for compatibility until this issue is fixed. See #213.

[BenjaminRodenberg]

Still open. Related to #222