Run xvfb around gradle tests

build.gradle.kts

plugins {
  kotlin("jvm")
  id("com.github.johnrengelman.processes") version "0.5.0"
}

val handle: Property<com.github.jengelman.gradle.plugins.processes.ProcessHandle> = project.objects.property()

val startXvfb by tasks.registering {
  val processHandle = project.procs.fork(closureOf<ExecSpec> {
    commandLine("/opt/X11/bin/Xvfb", ":99", "-ac")
  })
  handle.set(processHandle)
}

val stopXvfb by tasks.registering {
    handle.orNull?.abort()
}

val test by tasks.existing(Test::class) {
  dependsOn(startXvfb)
  environment["DISPLAY"] = ":99"
  finalizedBy(stopXvfb)
}