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waitUntil: Waiting for arbitrary conditions
===========================================
.. versionadded:: 2.0
Sometimes your tests need to wait a certain condition which does not trigger a signal, for example
that a certain control gained focus or a ``QListView`` has been populated with all items.
For those situations you can use :meth:`qtbot.waitUntil <pytestqt.plugin.QtBot.waitUntil>` to
wait until a certain condition has been met or a timeout is reached. This is specially important
in X window systems due to their asynchronous nature, where you can't rely on the fact that the
result of an action will be immediately available.
For example:
.. code-block:: python
def test_validate(qtbot):
window = MyWindow()
window.edit.setText("not a number")
# after focusing, should update status label
window.edit.setFocus()
assert window.status.text() == "Please input a number"
The ``window.edit.setFocus()`` may not be processed immediately, only in a future event loop, which
might lead to this test to work sometimes and fail in others (a *flaky* test).
A better approach in situations like this is to use ``qtbot.waitUntil`` with a callback with your
assertion:
.. code-block:: python
def test_validate(qtbot):
window = MyWindow()
window.edit.setText("not a number")
# after focusing, should update status label
window.edit.setFocus()
def check_label():
assert window.status.text() == "Please input a number"
qtbot.waitUntil(check_label)
``qtbot.waitUntil`` will periodically call ``check_label`` until it no longer raises
``AssertionError`` or a timeout is reached. If a timeout is reached, a
:class:`qtbot.TimeoutError <pytestqt.exceptions.TimeoutError>`
is raised from the last assertion error and the test will fail:
::
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
def check_label():
> assert window.status.text() == "Please input a number"
E AssertionError: assert 'OK' == 'Please input a number'
E - OK
E + Please input a number
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
> qtbot.waitUntil(check_label)
E pytestqt.exceptions.TimeoutError: waitUntil timed out in 1000 milliseconds
A second way to use ``qtbot.waitUntil`` is to pass a callback which returns ``True`` when the
condition is met or ``False`` otherwise. It is usually terser than using a separate callback with
``assert`` statement, but it produces a generic message when it fails because it can't make
use of ``pytest``'s assertion rewriting:
.. code-block:: python
def test_validate(qtbot):
window = MyWindow()
window.edit.setText("not a number")
# after focusing, should update status label
window.edit.setFocus()
qtbot.waitUntil(lambda: window.edit.hasFocus())
assert window.status.text() == "Please input a number"
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