test: added test cases for key-auth using admin API. (#121)

diff --git a/t/plugin/key-auth.t b/t/plugin/key-auth.t
index b4529bd..e7bd597 100644
--- a/t/plugin/key-auth.t
+++ b/t/plugin/key-auth.t
@@ -73,3 +73,79 @@
 done
 --- no_error_log
 [error]
+
+
+
+=== TEST 4: missing `key` of key-auth
+--- config
+    location /t {
+        content_by_lua_block {
+            local t = require("lib.test_admin").test
+            local code, body = t('/apisix/admin/routes/1',
+                 ngx.HTTP_PUT,
+                 [[{
+                        "plugins": {
+                            "key-auth": {
+                            }
+                        },
+                        "upstream": {
+                            "nodes": {
+                                "127.0.0.1:1980": 1
+                            },
+                            "type": "roundrobin"
+                        },
+                        "uri": "/hello"
+                }]]
+                )
+
+            if code >= 300 then
+                ngx.status = code
+            end
+            ngx.print(body)
+        }
+    }
+--- request
+GET /t
+--- error_code: 400
+--- response_body
+{"error_msg":"failed to check the configuration of plugin key-auth err: invalid \"required\" in docuement at pointer \"#\""}
+--- no_error_log
+[error]
+
+
+
+=== TEST 5: add key auth using admin api
+--- config
+    location /t {
+        content_by_lua_block {
+            local t = require("lib.test_admin").test
+            local code, body = t('/apisix/admin/routes/1',
+                 ngx.HTTP_PUT,
+                 [[{
+                        "plugins": {
+                            "key-auth": {
+                                "key": "auth-one"
+                            }
+                        },
+                        "upstream": {
+                            "nodes": {
+                                "127.0.0.1:1980": 1
+                            },
+                            "type": "roundrobin"
+                        },
+                        "uri": "/hello"
+                }]]
+                )
+
+            if code >= 300 then
+                ngx.status = code
+            end
+            ngx.say(body)
+        }
+    }
+--- request
+GET /t
+--- response_body
+passed
+--- no_error_log
+[error]