Improve test coverage (#4924)

Author: asvetlov

Lib/test/test_asyncio/test_transports.py

@@ -42,6 +42,7 @@ def test_not_implemented(self):
         self.assertRaises(NotImplementedError, transport.can_write_eof)
         self.assertRaises(NotImplementedError, transport.pause_reading)
         self.assertRaises(NotImplementedError, transport.resume_reading)
+        self.assertRaises(NotImplementedError, transport.is_reading)
         self.assertRaises(NotImplementedError, transport.close)
         self.assertRaises(NotImplementedError, transport.abort)