mirai code: Add tests for the message after last message element (#431)

mirai-serialization/src/commonTest/kotlin/net/mamoe/mirai/message/code/MiraiCodeParserTest.kt

@@ -24,6 +24,22 @@ internal class MiraiCodeParserTest {
         assertEquals(str, str.parseMiraiCode().toString())
     }
 
+    @Test
+    fun testAfter() {
+        val str = "sadvass][ [mirai:at:1,test]]vdsavs [mirai:atall]last"
+        val parse = str.parseMiraiCode()
+        assertEquals(str, parse.toString())
+        assertEquals("last", (parse.last() as? PlainText)?.content)
+    }
+
+    @Test
+    fun testBefore() {
+        val str = "sadvass][ [mirai:at:1,test]]vdsavs [mirai:atall]last"
+        val parse = str.parseMiraiCode()
+        assertEquals(str, parse.toString())
+        assertEquals("sadvass][ ", (parse.first() as? PlainText)?.content)
+    }
+
     @Test
     fun at() {
         val str = "[mirai:at:1,test]"