Prevent test_tab from creating user data dir.

This is another case (like test_qt_javascript) that needs redirection
of XDG_DATA_HOME to prevent Qt from creating ~/.share/local/qute_test.

tests/helpers/fixtures.py

@@ -432,3 +432,14 @@ def data_tmpdir(monkeypatch, tmpdir):
     os.mkdir(path)
     monkeypatch.setattr('qutebrowser.utils.standarddir.data', lambda: path)
     return tmpdir
+
+
+@pytest.fixture
+def redirect_xdg_data(data_tmpdir):
+    """Set XDG_DATA_HOME to a temp location.
+
+    While data_tmpdir covers most cases by redirecting standarddir.data(), this
+    is not enough for places Qt references the data dir internally. For these,
+    we need to set the environment variable to redirect data access.
+    """
+    os.putenv('XDG_DATA_HOME', str(data_tmpdir))

tests/unit/browser/test_tab.py

@@ -25,6 +25,8 @@ from qutebrowser.browser import browsertab
 from qutebrowser.keyinput import modeman
 from qutebrowser.utils import objreg
 
+pytestmark = pytest.mark.usefixtures('redirect_xdg_data')
+
 try:
     from PyQt5.QtWebKitWidgets import QWebView
 

tests/unit/browser/webkit/test_qt_javascript.py

@@ -21,7 +21,6 @@
 
 
 import pytest
-import os
 
 from PyQt5.QtCore import QObject, pyqtSignal
 from PyQt5.QtWebKit import QWebSettings
@@ -65,18 +64,14 @@ def test_element_js_webkit(webview, js_enabled, expected):
     assert result == expected
 
 
+@pytest.mark.usefixtures('redirect_xdg_data')
 @pytest.mark.parametrize('js_enabled, expected', [(True, 2.0), (False, 2.0)])
-def test_simple_js_webengine(qtbot, webengineview, js_enabled, expected,
-                             data_tmpdir):
+def test_simple_js_webengine(qtbot, webengineview, js_enabled, expected):
     """With QtWebEngine, runJavaScript works even when JS is off."""
     # pylint: disable=no-name-in-module,useless-suppression
     # If we get there (because of the webengineview fixture) we can be certain
     # QtWebEngine is available
     from PyQt5.QtWebEngineWidgets import QWebEngineSettings
-    # runJavaScript will write to the data directory. As the path is determined
-    # by Qt and bypasses standarddir.data(), the data_tmpdir fixture is not
-    # enough -- we need to set XDG_DATA_HOME as well
-    os.putenv('XDG_DATA_HOME', str(data_tmpdir))
     webengineview.settings().setAttribute(QWebEngineSettings.JavascriptEnabled,
                                           js_enabled)