Check for license headers in kotlin source files

pmd-lang-test/pom.xml

@@ -18,6 +18,15 @@
 
     <build>
         <sourceDirectory>${project.basedir}/src/main/kotlin</sourceDirectory>
+        <testResources>
+            <testResource>
+                <directory>${project.basedir}/src/test/resources</directory>
+            </testResource>
+            <!-- Adding kotlin files to test resources, so that checkstyle verifies the license header -->
+            <testResource>
+                <directory>${project.basedir}/src/main/kotlin</directory>
+            </testResource>
+        </testResources>
         <plugins>
             <!-- The kotlin plugin has to run before the java plugin-->
             <plugin>