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waitCallback: Waiting for methods taking a callback
===================================================
.. versionadded:: 3.1
Some methods in Qt (especially ``QtWebEngine``) take a callback as argument,
which gets called by Qt once a given operation is done.
To test such code, you can use :meth:`qtbot.waitCallback <pytestqt.plugin.QtBot.waitCallback>`
which waits until the callback has been called or a timeout is reached.
The ``qtbot.waitCallback()`` method returns a callback which is callable
directly.
For example:
.. code-block:: python
def test_js(qtbot):
page = QWebEnginePage()
with qtbot.waitCallback() as cb:
page.runJavaScript("1 + 1", cb)
cb.assert_called_with(2) # result of the last js statement
Anything following the ``with`` block will be run only after the callback has been called.
If the callback doesn't get called during the given timeout,
:class:`qtbot.TimeoutError <pytestqt.exceptions.TimeoutError>` is raised. If it is called more than once,
:class:`qtbot.CallbackCalledTwiceError <pytestqt.wait_signal.CallbackCalledTwiceError>` is raised.
raising parameter
-----------------
Similarly to ``qtbot.waitSignal``, you can pass a ``raising=False`` parameter
(or set the ``qt_default_raising`` ini option) to avoid raising an exception on
timeouts. See :doc:`signals` for details.
Getting arguments the callback was called with
----------------------------------------------
After the callback is called, the arguments and keyword arguments passed to it
are available via ``.args`` (as a list) and ``.kwargs`` (as a dict),
respectively.
In the example above, we could check the result via:
.. code-block:: python
assert cb.args == [2]
assert cb.kwargs == {}
Instead of checking the arguments by hand, you can use ``.assert_called_with()``
to make sure the callback was called with the given arguments:
.. code-block:: python
cb.assert_called_with(2)
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