Added same unittest hair as the other test modules.

src/supervisor/tests/test_loggers.py

@@ -294,3 +294,10 @@ class DummyHandler:
     def close(self):
         self.closed = True
 
+
+def test_suite():
+    return unittest.findTestCases(sys.modules[__name__])
+
+if __name__ == '__main__':
+    unittest.main(defaultTest='test_suite')
+