Remove arguments to try and diagnose the issue at a deeper level

Dockerfile

@@ -5,6 +5,5 @@ RUN apt-get update && apt-get install -y \
     gpg \
     xvfb \
     libxrender1 libxtst6 libxi6 libxext6
-RUN export MAVEN_OPTS="-Djava.awt.headless=true"
 RUN /usr/bin/Xvfb :99 &
 RUN export DISPLAY=:99

Jenkinsfile

@@ -32,7 +32,7 @@ pipeline {
         stage("Test") {
             steps {
                 wrap([$class: 'Xvfb']) {
-                    sh "mvn test -Djava.awt.headless=true"
+                    sh "mvn test"
                 }
             }
             post {