Add a test for a None currentWidget with backforward widget

qutebrowser/mainwindow/statusbar/backforward.py

@@ -29,7 +29,9 @@ class Backforward(textbase.TextBase):
     def on_tab_cur_url_changed(self, tabs):
         """Called on URL changes."""
         tab = tabs.currentWidget()
-        if tab is None:  # pragma: no cover
+        if tab is None:
+            self.setText('')
+            self.hide()
             return
         text = ''
         if tab.history.can_go_back():

tests/helpers/stubs.py

@@ -620,7 +620,10 @@ class TabbedBrowserStub(QObject):
         return self.current_index
 
     def currentWidget(self):
-        return self.tabs[self.currentIndex() - 1]
+        idx = self.currentIndex()
+        if idx == -1:
+            return None
+        return self.tabs[idx - 1]
 
     def tabopen(self, url):
         self.opened_url = url

tests/unit/mainwindow/statusbar/test_backforward.py

@@ -56,3 +56,21 @@ def test_backforward_widget(backforward_widget, stubs,
         backforward_widget.on_tab_cur_url_changed(tabbed_browser)
         assert backforward_widget.text() == ''
         assert not backforward_widget.isVisible()
+
+
+def test_none_tab(backforward_widget, stubs, fake_web_tab):
+    """Make sure nothing crashes when passing None as tab."""
+    tab = fake_web_tab(can_go_back=True, can_go_forward=True)
+    tabbed_browser = stubs.TabbedBrowserStub()
+    tabbed_browser.current_index = 1
+    tabbed_browser.tabs = [tab]
+    backforward_widget.on_tab_cur_url_changed(tabbed_browser)
+
+    assert backforward_widget.text() == '[<>]'
+    assert backforward_widget.isVisible()
+
+    tabbed_browser.current_index = -1
+    backforward_widget.on_tab_cur_url_changed(tabbed_browser)
+
+    assert backforward_widget.text() == ''
+    assert not backforward_widget.isVisible()