unittest: Add test for environment isolation.

python-stdlib/unittest/test_unittest.py

@@ -1,4 +1,5 @@
 import unittest
+from test_unittest_isolated import global_context
 
 
 class TestUnittestAssertions(unittest.TestCase):
@@ -142,6 +143,11 @@ class TestUnittestAssertions(unittest.TestCase):
         else:
             self.fail("Unexpected success was not detected")
 
+    def test_NotChangedByOtherTest(self):
+        global global_context
+        assert global_context is None
+        global_context = True
+
 
 if __name__ == "__main__":
     unittest.main()

python-stdlib/unittest/test_unittest_isolated.py

@@ -0,0 +1,15 @@
+import unittest
+
+
+global_context = None
+
+
+class TestUnittestIsolated(unittest.TestCase):
+    def test_NotChangedByOtherTest(self):
+        global global_context
+        assert global_context is None
+        global_context = True
+
+
+if __name__ == "__main__":
+    unittest.main()