add unittest: variables in testcase teststep should override api's

tests/api/basic.yml

@@ -17,6 +17,10 @@
 
 - api:
     def: create_user($uid, $user_name, $user_password, $token)
+    variables:
+        - user_name: user0
+        - user_password: "000000"
+        - uid: 2000
     request:
         url: /api/users/$uid
         method: POST