Index: Lib/importlib/test/source/test_abc_loader.py
===================================================================
--- Lib/importlib/test/source/test_abc_loader.py	(revision 72457)
+++ Lib/importlib/test/source/test_abc_loader.py	(working copy)
@@ -250,14 +250,14 @@
     @source_util.writes_bytecode
     def verify_bytecode(self, mock, name):
         assert name in mock.module_paths
-        self.assert_(name in mock.module_bytecode)
+        self.assertIn(name, mock.module_bytecode)
         magic = mock.module_bytecode[name][:4]
         self.assertEqual(magic, imp.get_magic())
         mtime = importlib._r_long(mock.module_bytecode[name][4:8])
         self.assertEqual(mtime, 1)
         bc = mock.module_bytecode[name][8:]
+        self.assertEqual(bc, mock.compile_bc(name))
 
-
     def test_module(self):
         mock, name = super().test_module()
         self.verify_bytecode(mock, name)
Index: Lib/importlib/test/source/test_case_sensitivity.py
===================================================================
--- Lib/importlib/test/source/test_case_sensitivity.py	(revision 72457)
+++ Lib/importlib/test/source/test_case_sensitivity.py	(working copy)
@@ -36,18 +36,18 @@
         with test_support.EnvironmentVarGuard() as env:
             env.unset('PYTHONCASEOK')
             sensitive, insensitive = self.sensitivity_test()
-            self.assert_(hasattr(sensitive, 'load_module'))
-            self.assert_(self.name in sensitive._base_path)
-            self.assert_(insensitive is None)
+            self.assertTrue(hasattr(sensitive, 'load_module'))
+            self.assertIn(self.name, sensitive._base_path)
+            self.assertIsNone(insensitive)
 
     def test_insensitive(self):
         with test_support.EnvironmentVarGuard() as env:
             env.set('PYTHONCASEOK', '1')
             sensitive, insensitive = self.sensitivity_test()
-            self.assert_(hasattr(sensitive, 'load_module'))
-            self.assert_(self.name in sensitive._base_path)
-            self.assert_(hasattr(insensitive, 'load_module'))
-            self.assert_(self.name in insensitive._base_path)
+            self.assertTrue(hasattr(sensitive, 'load_module'))
+            self.assertIn(self.name, sensitive._base_path)
+            self.assertTrue(hasattr(insensitive, 'load_module'))
+            self.assertIn(self.name, insensitive._base_path)
 
 
 def test_main():
Index: Lib/importlib/test/util.py
===================================================================
--- Lib/importlib/test/util.py	(revision 72457)
+++ Lib/importlib/test/util.py	(working copy)
@@ -7,17 +7,18 @@
 
 
 def case_insensitive_tests(class_):
-    """Class decorator that nullifies tests that require a case-insensitive
+    """Class decorator that nullifies tests requiring a case-insensitive
     file system."""
-    if sys.platform not in ('win32', 'darwin', 'cygwin'):
-        original_name = os.listdir('.')[0]
-        if original_name.upper() != original_name:
-            changed_name = original_name.upper()
-        else:
-            changed_name = original_name.lower()
+    # Windows is the only OS that is *always* case-insensitive
+    # (OS X *can* be case-sensitive).
+    if sys.platform not in ('win32', 'cygwin'):
+        changed_name = __file__.upper()
+        if changed_name == __file__:
+            changed_name = __file__.lower()
         if os.path.exists(changed_name):
             return class_
-        return unittest.TestCase
+        else:
+            return unittest.TestCase
     else:
         return class_
 
Index: Lib/importlib/test/extension/test_case_sensitivity.py
===================================================================
--- Lib/importlib/test/extension/test_case_sensitivity.py	(revision 72457)
+++ Lib/importlib/test/extension/test_case_sensitivity.py	(working copy)
@@ -20,13 +20,13 @@
         with support.EnvironmentVarGuard() as env:
             env.unset('PYTHONCASEOK')
             loader = self.find_module()
-            self.assert_(loader is None)
+            self.assertIsNone(loader)
 
     def test_case_insensitivity(self):
         with support.EnvironmentVarGuard() as env:
             env.set('PYTHONCASEOK', '1')
             loader = self.find_module()
-            self.assert_(hasattr(loader, 'load_module'))
+            self.assertTrue(hasattr(loader, 'load_module'))