add missing license
diff --git a/jspwiki-util/src/test/java/org/apache/wiki/util/comparators/PrincipalComparatorTest.java b/jspwiki-util/src/test/java/org/apache/wiki/util/comparators/PrincipalComparatorTest.java
index dfbf187..7aa136f 100644
--- a/jspwiki-util/src/test/java/org/apache/wiki/util/comparators/PrincipalComparatorTest.java
+++ b/jspwiki-util/src/test/java/org/apache/wiki/util/comparators/PrincipalComparatorTest.java
@@ -1,3 +1,21 @@
+/*
+ Licensed to the Apache Software Foundation (ASF) under one
+ or more contributor license agreements. See the NOTICE file
+ distributed with this work for additional information
+ regarding copyright ownership. The ASF licenses this file
+ to you under the Apache License, Version 2.0 (the
+ "License"); you may not use this file except in compliance
+ with the License. You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing,
+ software distributed under the License is distributed on an
+ "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ KIND, either express or implied. See the License for the
+ specific language governing permissions and limitations
+ under the License.
+ */
package org.apache.wiki.util.comparators;
import org.junit.jupiter.api.Assertions;