Scanning leaves loaded modules

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This can shadow bugs where a module is accessed as an attribute of a package. Is there a way to "unport" modules? Deleting them from sys.modules leaves the attributes intact.

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I'm not sure if it is sanely possible to "unimport" in Python. Perhaps the default scanning should be limited to packages named 'tests' (including subpackages). This goes against the original ideals of Attest but might be sensible for a default. This is really only about when you run "attest" with no arguments specifying the location of the tests.