test(json): cover duplicate field names

Author: halibobo1205

framework/src/test/java/org/tron/json/JsonTest.java

@@ -26,6 +26,12 @@ public void testUnquotedFieldNames() {
     assertEquals(1, JSON.parseObject("{a:1}").getIntValue("a"));
   }
 
+  @Test
+  public void testDupFieldNames() {
+    assertEquals(2, JSON.parseObject("{a:1, a:2 }").getIntValue("a"));
+    assertEquals(1, JSON.parseObject("{a:2, a:1 }").getIntValue("a"));
+  }
+
   @Test
   public void testSingleQuotes() {
     assertEquals(1,  JSON.parseObject("{'a':'1'}").getIntValue("a"));