Hi, I've enabled xvfb for both Travis and Jenkins, and it enables us to run both headless=true and headless=false builds.
Sample coverage improvement: https://codecov.io/gh/apache/jmeter/branch/master/history/src/core/src/main/java/org/apache/jmeter/gui/HtmlReportUI.java?before=00fd8f09d578157cc9db5eb6c5e084c89a475d3f The same thing on Sonarcloud: https://sonarcloud.io/code?id=JMeter&selected=JMeter%3Asrc%2Fcore%2Fsrc%2Fmain%2Fjava%2Forg%2Fapache%2Fjmeter%2Fgui%2FHtmlReportUI.java Vladimir
