Note for myself:

In case you get such error

java.lang.IllegalStateException: Test runner could not locate test class [org.jboss.windup.addon.ui.WindupUpdateDistributionCommandXTest] in any deployed Addon - Reason unknown.

at org.jboss.forge.arquillian.impl.FurnaceTestMethodExecutor.invoke(FurnaceTestMethodExecutor.java:272)

It's because the test is using a simple Furnace container by default, and you rather need the CDI container, i.e.

{
    @Deployment
    @AddonDependencies({
        @AddonDependency(name = "org.jboss.forge.furnace.container:cdi"),

Would be nice if Furnace told you something along the lines of  "You are using the simple container, that means services should be registered as documented at http://..."

HTH