Add an inheritance test for importlib.abc.SourceLoader.
diff --git a/Lib/importlib/test/test_abc.py b/Lib/importlib/test/test_abc.py
index 5229ba4..0ecbe39 100644
--- a/Lib/importlib/test/test_abc.py
+++ b/Lib/importlib/test/test_abc.py
@@ -59,6 +59,11 @@
     subclasses = [abc.PyLoader]
 
 
+class SourceLoader(InheritanceTests, unittest.TestCase):
+
+    superclasses = [abc.ResourceLoader, abc.ExecutionLoader]
+
+
 class PyLoader(InheritanceTests, unittest.TestCase):
 
     superclasses = [abc.Loader, abc.ResourceLoader, abc.ExecutionLoader]