Add a testcase for Command

tests/test_cmd.py

@@ -0,0 +1,10 @@
+from tornado.ioloop import IOLoop
+from tests.helper import ExternalVersionTestCase
+
+
+class CMDTest(ExternalVersionTestCase):
+    def get_new_ioloop(self):
+        return IOLoop.instance()
+
+    def test_cmd(self):
+        self.assertEqual(self.sync_get_version("example", {"cmd": "echo Meow"}), "Meow")