The text clearly seems to be referencing `TestFuncAcceptsSequencesMixin`,
for which no target is available. Name the class properly and suppress
the dangling reference.
arg = (1, 2, 3)
When using this pattern, remember that all classes that inherit from
- :class:`unittest.TestCase` are run as tests. The :class:`Mixin` class in the example above
+ :class:`unittest.TestCase` are run as tests. The :class:`!TestFuncAcceptsSequencesMixin` class in the example above
does not have any data and so can't be run by itself, thus it does not
inherit from :class:`unittest.TestCase`.