added test for Json::encode() and JsonSerializable

tests/unit/framework/helpers/JsonTest.php

@@ -2,6 +2,7 @@
 
 namespace yiiunit\framework\helpers;
 
+use yii\base\Model;
 use yii\helpers\Json;
 use yiiunit\TestCase;
 use yii\web\JsExpression;
@@ -48,6 +49,10 @@ class JsonTest extends TestCase
         // https://github.com/yiisoft/yii2/issues/957
         $data = (object) null;
         $this->assertSame('{}', Json::encode($data));
+
+        // JsonSerializable
+        $data = new JsonModel();
+        $this->assertSame('{"json":"serializable"}', Json::encode($data));
     }
 
     public function testDecode()
@@ -66,3 +71,11 @@ class JsonTest extends TestCase
         Json::decode($json);
     }
 }
+
+class JsonModel extends Model implements \JsonSerializable
+{
+    function jsonSerialize()
+    {
+        return ['json' => 'serializable'];
+    }
+}
\ No newline at end of file