Update TestTextBuffer.java

Author: pjfanning

src/test/java/com/fasterxml/jackson/core/util/TestTextBuffer.java

@@ -1,5 +1,7 @@
 package com.fasterxml.jackson.core.util;
 
+import org.junit.jupiter.api.Test;
+
 import java.io.IOException;
 
 import static org.junit.jupiter.api.Assertions.*;