Add System-rules library to root pom

Used to mock environment variable injection setting during build-time
diff --git a/pom.xml b/pom.xml
index ded1cd4..3142ce7 100644
--- a/pom.xml
+++ b/pom.xml
@@ -839,6 +839,14 @@
                 <scope>test</scope>
             </dependency>
 
+            <!-- System Rules for unit testing -->
+            <dependency>
+                <groupId>com.github.stefanbirkner</groupId>
+                <artifactId>system-rules</artifactId>
+                <version>1.19.0</version>
+                <scope>test</scope>
+            </dependency>
+
             <!-- Saxon -->
             <dependency>
                 <groupId>net.sf.saxon</groupId>