Currently assertRaises(), assertRaisesRegex(), assertWarns() and assertWarnsRegex() have some weird behavior. # always success if the callable is None self.assertRaises(SomeException, None) # keyword arguments except "msg" are ignored with self.assertRaises(SomeException, foobar=123): ... # always success because keyword arguments are ignored self.assertRaises(SomeException, callable=func) Hardly any user code uses these "features" intentionally. More likely such examples are hidden bugs (see for example [1]). A DeprecationWarning is raised in these cases since 3.5 (issue24134), and it is time to make them errors. [1] https://mail.python.org/pipermail/python-list/2018-July/736363.html

 New changeset 77d5781835b6e0a132694ebadc22b1cbdb9913f8 by Serhiy Storchaka in branch 'master': bpo-34318: Convert deprecation warnings to errors in assertRaises() etc. (GH-8623) https://github.com/python/cpython/commit/77d5781835b6e0a132694ebadc22b1cbdb9913f8