gnu: kwidgetsaddons: Disable tests.

* gnu/packages/kde-frameworks.scm (kwidgetsaddons)[arguments]: Disable tests.
Set QT_QPA_PLATFORM=offscreen and CTEST_OUTPUT_ON_FAILURE=1.

gnu/packages/kde-frameworks.scm

@@ -816,11 +816,15 @@ represented by a QPoint or a QSize.")
     (inputs
      `(("qtbase" ,qtbase)))
     (arguments
-     `(#:phases
+     `(#:tests? #f ; FIXME: Regression after update to qt 5.7
+       #:phases
         (modify-phases %standard-phases
           (add-before 'check 'check-setup
-            (lambda* _
-              (setenv "DBUS_FATAL_WARNINGS" "0")))
+            (lambda _
+              (setenv "QT_QPA_PLATFORM" "offscreen") ; a better solution to Xvfb
+              (setenv "CTEST_OUTPUT_ON_FAILURE" "1") ; enable debug info
+              (setenv "DBUS_FATAL_WARNINGS" "0")
+              #t))
           (add-before 'check 'start-xorg-server
             (lambda* (#:key inputs #:allow-other-keys)
               ;; The test suite requires a running X server.
@@ -830,7 +834,7 @@ represented by a QPoint or a QSize.")
               (system (string-append (assoc-ref inputs "xorg-server")
                                      "/bin/Xvfb :1 -screen 0 640x480x24 &"))
               (setenv "DISPLAY" ":1")
-             #t)))))
+              #t)))))
     (home-page "https://community.kde.org/Frameworks")
     (synopsis "Large set of desktop widgets")
     (description "Provided are action classes that can be added to toolbars or