Test Completer.schedule_completion_update.

update_completion is only used internally, so instead test the real
public entry point which is schedule_completion_update.

This required mocking out QTimer to fire immediately so the test didn't
have to do flaky artificial delays.

tests/helpers/stubs.py

@@ -381,6 +381,28 @@ class FakeTimer(QObject):
         return self._started
 
 
+class InstaTimer(QObject):
+
+    """Stub for a QTimer that fires instantly on start().
+
+    Useful to test a time-based event without inserting an artificial delay.
+    """
+
+    timeout = pyqtSignal()
+
+    def __init__(self, parent=None):
+        super().__init__(parent)
+
+    def start(self):
+        self.timeout.emit()
+
+    def setSingleShot(self, yes):
+        pass
+
+    def setInterval(self, interval):
+        pass
+
+
 class FakeConfigType:
 
     """A stub to provide valid_values for typ attribute of a SettingValue."""

tests/unit/completion/test_completer.py

@@ -48,8 +48,10 @@ def cmd(stubs, qtbot):
 
 
 @pytest.fixture
-def completer_obj(qtbot, cmd, config_stub):
+def completer_obj(qtbot, cmd, config_stub, monkeypatch, stubs):
     """Create the completer used for testing."""
+    monkeypatch.setattr('qutebrowser.completion.completer.QTimer',
+        stubs.InstaTimer)
     config_stub.data = {'completion': {'auto-open': False}}
     return completer.Completer(cmd, 0)
 
@@ -162,7 +164,7 @@ def test_update_completion(txt, expected, cmd, completer_obj,
     """Test setting the completion widget's model based on command text."""
     # this test uses | as a placeholder for the current cursor position
     _set_cmd_prompt(cmd, txt)
-    completer_obj.update_completion()
+    completer_obj.schedule_completion_update()
     if expected is None:
         assert not completion_widget_stub.set_model.called
     else: