[Update] Framework-API 在 MessageChainTest 补充测试项;

[Update] MessageChainTest 补充 'plusMessageTest' 测试项;

ContentGrabbingJi-framework-api/src/test/java/net/lamgc/cgj/bot/framework/message/MessageChainTest.java

@@ -90,6 +90,13 @@ public class MessageChainTest {
         Assert.assertEquals("BotCode: [test:arg=value].", chain.contentToString());
     }
 
+    @Test
+    public void plusMessageTest() {
+        MessageChain chain = new MessageChain("This ", "is ", "a ");
+        chain.plus(new CharSequenceMessage("simple message."));
+        Assert.assertEquals("This is a simple message.", chain.contentToString());
+    }
+
     @Test
     public void deleteTest() {
         final String[] contents = new String[] {"This", " is ", "a ", "simple", " message."};