[telemetry] Print browser standard output and log upon BrowserTestCase failures

telemetry/telemetry/testing/browser_test_case.py

Index: telemetry/telemetry/testing/browser_test_case.py
diff --git a/telemetry/telemetry/testing/browser_test_case.py b/telemetry/telemetry/testing/browser_test_case.py
index 85e6797223392acc4cf2c743cc83a9c130bf3ed9..710904b07ef7c31110f1ba308c35888d7561272c 100644
--- a/telemetry/telemetry/testing/browser_test_case.py
+++ b/telemetry/telemetry/testing/browser_test_case.py
@@ -2,7 +2,11 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+from functools import wraps
+import logging
 import os
+import sys
+import types
 import unittest
 
 from telemetry.internal.browser import browser_finder
@@ -13,6 +17,52 @@ current_browser_options = None
 current_browser = None
 
 
+class _MetaBrowserTestCase(type):
+  """Metaclass for BrowserTestCase.
+
+  The metaclass wraps all test* methods of all subclasses of BrowserTestCase to
+  print browser standard output and log upon failure.
+  """
+
+  def __new__(mcs, name, bases, dct):
+    new_dct = {}
+    for attributeName, attribute in dct.iteritems():
+      if (isinstance(attribute, types.FunctionType) and
+          attributeName.startswith('test')):
+        attribute = mcs._PrintBrowserStandardOutputAndLogOnFailure(attribute)
+      new_dct[attributeName] = attribute
+    return type.__new__(mcs, name, bases, new_dct)
+
+  @staticmethod
+  def _PrintBrowserStandardOutputAndLogOnFailure(method):
+    @wraps(method)
+    def WrappedMethod(self):
+      try:  # pylint: disable=broad-except
+        method(self)
+      except Exception:
+        exc_info = sys.exc_info()
+
+        logging.info('*************** BROWSER STANDARD OUTPUT ***************')
+        try:  # pylint: disable=broad-except
+          logging.info(self._browser.GetStandardOutput())
+        except Exception:
+          logging.exception('Failed to get browser standard output:')
+        logging.info('*********** END OF BROWSER STANDARD OUTPUT ************')
+
+        logging.info('********************* BROWSER LOG *********************')
+        try:  # pylint: disable=broad-except
+          logging.info(self._browser.GetLogFileContents())
+        except Exception:
+          logging.exception('Failed to get browser log:')
+        logging.info('***************** END OF BROWSER LOG ******************')
+
+        # Re-raise the original exception. Note that we can't just use 'raise'
+        # without any arguments because an exception might have been thrown when
+        # the browser standard output was retrieved.
+        raise exc_info[0], exc_info[1], exc_info[2]
+    return WrappedMethod
+
+
 def teardown_browser():
   global current_browser
   global current_browser_options
@@ -24,6 +74,8 @@ def teardown_browser():
 
 
 class BrowserTestCase(unittest.TestCase):
+  __metaclass__ = _MetaBrowserTestCase
+
   @classmethod
   def setUpClass(cls):
     cls._platform = None