When DeprecationWarning was hidden by default, the expectation was that 3rd party test runners would follow the unittest module's lead and re-enable them when running tests (see https://docs.python.org/3/whatsnew/2.7.html#changes-to-the-handling-of-deprecation-warnings and and https://docs.python.org/3/library/unittest.html#unittest.TextTestRunner)

This currently isn't the case for pytest - it requires developers to explicitly opt-in to seeing deprecation warnings, rather than requiring them to opt-out the way unittest does.