The replacement is TestLoader().loadTestsFromTestCase(), and it's
already in a prominent place in the docs:

"""
Instead of :func:`unittest.main`, there are other ways to run the tests
with a
finer level of control, less terse output, and no requirement to be run
from the
command line.  For example, the last two lines may be replaced with::

   suite =
unittest.TestLoader().loadTestsFromTestCase(TestSequenceFunctions)
   unittest.TextTestRunner(verbosity=2).run(suite)
"""

Closing as "works for me".