Use pytest for test discovery in build_ext

setuptools/tests/test_build_ext.py

 """build_ext tests
 """
-import unittest
 import distutils.command.build_ext as orig
 
 from setuptools.command.build_ext import build_ext
 from setuptools.dist import Distribution
 
-class TestBuildExtTest(unittest.TestCase):
+class TestBuildExt:
 
     def test_get_ext_filename(self):
         """