Make test failure messages more verbose (and thus useful to testing operators).

client/site_tests/factory_Leds/factory_Leds.py

 # -*- coding: utf-8 -*-
 #
 # Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 
 # DESCRIPTION :
 #
 # This is a factory test to test the LEDs (wifi, battery, etc).
@@ skipping 159 matching lines @@
 
     def register_callbacks(self, window):
         window.connect('key-release-event', self.key_release_callback)
         window.add_events(gdk.KEY_RELEASE_MASK)
 
     def run_once(self, led_ctl_path=None):
 
         factory.log('%s run_once' % self.__class__)
 
         self._led_ctl_path = led_ctl_path
+        if not os.path.exists(self._led_ctl_path):
+            raise error.TestNAError('Command %s does not exist' %
+                                    self._led_ctl_path)
 
         self._shift_color = ful.BLACK
         self._shift_cnt = 0
 
         os.chdir(self.srcdir)
-        image = cairo.ImageSurface.create_from_png('leds.png')
+        try:
+            image = cairo.ImageSurface.create_from_png('leds.png')
+        except cairo.Error as e:
+            raise error.TestNAError('Error while opening leds.png: %s' %
+                                    e.message)
         image_size = (image.get_width(), image.get_height())
         self._leds_image = image
 
         image = cairo.ImageSurface.create_from_png('shf.png')
         self._shf_image = image
 
         self._pattern_queue = [x for x in reversed(_PATTERN_LIST)]
         self._status_map = dict((n, ful.UNTESTED) for n, f in _PATTERN_LIST)
 
         pattern_da = gtk.DrawingArea()
@@ skipping 32 matching lines @@
             cleanup_callback=self.quit)
 
         failed_set = set(name for name, status in self._status_map.items()
                          if status is not ful.PASSED)
         if failed_set:
             raise error.TestFail('Some patterns failed\n' \
                                  '以下圖樣測試未通過: %s' %
                                  ', '.join(failed_set))
 
         factory.log('%s run_once finished' % self.__class__)