Demonstrates a problem with pytest that I can't figure out.

There is a test class, TestDomain, in the tests folder that is correctly automatically detected. There is a domain class, Testament, in the source folder, that causes a warning:

src/pytest_collection_issue/domain.py:6
  src/pytest_collection_issue/domain.py:6: PytestCollectionWarning: cannot collect test class 'Testament' because it has a __init__ constructor (from: tests/test_domain.py)
    class Testament(object):

After many Google searches, I have tried a variety of things to get pytest to ignore things found in src. I understand that I could tag each object starting with Test with __test__ = False, but in my real project there will be a lot of those. I'd like to find some way to tell pytest once that it should never treat anything in the src directory as a test. Or, equivalently, to tell it only look in tests.