Bug 1539449 - [marionette] Suppress Gecko output in test_crash.py to prevent mozharness failure, r=whimboo

Differential Revision: https://phabricator.services.mozilla.com/D32169

--HG--
extra : moz-landing-system : lando

testing/marionette/harness/marionette_harness/tests/unit/test_crash.py

@@ -2,13 +2,15 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-from __future__ import absolute_import
+from __future__ import absolute_import, print_function
 
 import glob
 import os
 import platform
 import shutil
+import sys
 import unittest
+from io import StringIO
 
 from marionette_driver import Wait
 from marionette_driver.errors import (
@@ -99,6 +101,25 @@ class BaseCrashTestCase(MarionetteTestCase):
 
 class TestCrash(BaseCrashTestCase):
 
+    def setUp(self):
+        if os.environ.get('MOZ_AUTOMATION'):
+            # Capture stdout, otherwise the Gecko output causes mozharness to fail
+            # the task due to "A content process has crashed" appearing in the log.
+            # To view stdout for debugging, use `print(self.new_out.getvalue())`
+            print("Suppressing GECKO output. To view, add `print(self.new_out.getvalue())` "
+                  "to the end of this test.")
+            self.new_out, self.new_err = StringIO(), StringIO()
+            self.old_out, self.old_err = sys.stdout, sys.stderr
+            sys.stdout, sys.stderr = self.new_out, self.new_err
+
+        super(TestCrash, self).setUp()
+
+    def tearDown(self):
+        super(TestCrash, self).tearDown()
+
+        if os.environ.get('MOZ_AUTOMATION'):
+            sys.stdout, sys.stderr = self.old_out, self.old_err
+
     @unittest.skipIf(platform.machine() == "ARM64" and platform.system() == "Windows",
                      "Bug 1540784 - crashreporter related issues on Windows 10 aarch64. ")
     def test_crash_chrome_process(self):