Fix a flaky test caused by caching of UserPartition schemes

common/lib/xmodule/xmodule/partitions/tests/test_partitions.py

@@ -131,6 +131,9 @@ class PartitionTestCase(TestCase):
             extensions, namespace=USER_PARTITION_SCHEME_NAMESPACE
         )
 
+        # Be sure to clean up the global scheme_extensions after the test.
+        self.addCleanup(self.cleanupSchemeExtensions)
+
         # Create a test partition
         self.user_partition = UserPartition(
             self.TEST_ID,
@@ -145,6 +148,9 @@ class PartitionTestCase(TestCase):
         self.user_partition.get_scheme(self.non_random_scheme.name)
         self.user_partition.get_scheme(self.random_scheme.name)
 
+    def cleanupSchemeExtensions(self):
+        UserPartition.scheme_extensions = None
+
 
 class TestUserPartition(PartitionTestCase):
     """Test constructing UserPartitions"""