Use start-stop deamon

.travis.yml

@@ -1,6 +1,11 @@
 language: php
 dist: xenial
 
+# Since Xenial services are not started by default, we need to instruct it below to start.
+services:
+  - xvfb
+  - mysql
+
 sudo: false
 
 cache:
@@ -16,11 +21,6 @@ php:
   - 7.2
   - 7.3
 
-# Since Xenial services are not started by default, we need to instruct it below to start.
-services:
-  - mysql
-  - xvfb
-
 env:
   - WP_VERSION=latest WP_MULTISITE=0
 
@@ -66,9 +66,7 @@ before_script:
       bash tests/bin/install.sh woocommerce_test root '' localhost $WP_VERSION
       composer global require "phpunit/phpunit=5.7.*|7.5.*"
     fi
-  - export DISPLAY=:99.0
-  - sh -e /etc/init.d/xvfb start
-  - sleep 3 # give xvfb some time to start
+  - "/sbin/start-stop-daemon --start --quiet --pidfile /tmp/custom_xvfb_99.pid --make-pidfile --background --exec /usr/bin/Xvfb -- :99 -ac -screen 0 1280x1024x16"
 
 script:
   - bash tests/bin/phpunit.sh