Restore Python 2 compatibility.

Author: jaraco

setup.cfg

@@ -41,6 +41,7 @@ testing =
     importlib_resources>=1.3; python_version < "3.9"
     packaging
     pep517
+    unittest2; python_version < "3"
 docs =
     sphinx
     rst.linker

tests/test_api.py

@@ -1,6 +1,10 @@
 import re
 import textwrap
-import unittest
+
+try:
+    import unittest2 as unittest
+except ImportError:
+    import unittest
 
 from . import fixtures
 from importlib_metadata import (