Add missing dependencies

Author: ppkarwasz

log4j-plugins-test/pom.xml

@@ -58,6 +58,11 @@
       <artifactId>log4j-api-test</artifactId>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>org.assertj</groupId>
+      <artifactId>assertj-core</artifactId>
+      <scope>test</scope>
+    </dependency>
     <dependency>
       <groupId>org.hamcrest</groupId>
       <artifactId>hamcrest</artifactId>