Add test dependency on Mockito

pom.xml

@@ -292,6 +292,13 @@
       <type>jar</type>
       <optional>false</optional>
     </dependency>
+    <!-- test dependencies -->
+    <dependency>
+      <groupId>org.mockito</groupId>
+      <artifactId>mockito-core</artifactId>
+      <version>2.7.0</version>
+      <scope>test</scope>
+    </dependency>
     <dependency>
       <groupId>junit</groupId>
       <artifactId>junit</artifactId>