Bug 1512336 - [marionette] Fix hang in TestNavigate.test_set_location_through_execute_script. r=ato

An unexpected remoteness change can cause the
"WebDriver:FindElement" command to hang forever.
To avoid that already pre-load a web page which
enables the remoteness flag.

Differential Revision: https://phabricator.services.mozilla.com/D16306

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

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

@@ -116,17 +116,17 @@ class BaseNavigationTestCase(WindowManagerMixin, MarionetteTestCase):
 class TestNavigate(BaseNavigationTestCase):
 
     def test_set_location_through_execute_script(self):
-        test_element_locator = (By.ID, "testh1")
+        # To avoid unexpected remoteness changes and a hang in any non-navigation
+        # command (bug 1519354) when navigating via the location bar, already
+        # pre-load a page which causes a remoteness change.
+        self.marionette.navigate(self.test_page_push_state)
 
         self.marionette.execute_script(
             "window.location.href = arguments[0];",
             script_args=(self.test_page_remote,), sandbox=None)
 
-        # We cannot use get_url() to wait until the target page has been loaded,
-        # because it will return the URL of the top browsing context and doesn't
-        # wait for the page load to be complete.
         Wait(self.marionette, timeout=self.marionette.timeout.page_load).until(
-            expected.element_present(*test_element_locator),
+            expected.element_present(*(By.ID, "testh1")),
             message="Target element 'testh1' has not been found")
 
         self.assertEqual(self.test_page_remote, self.marionette.get_url())