.. _`warnings`: Warnings Capture ================ .. versionadded:: 3.1 Starting from version ``3.1``, pytest now automatically catches warnings during test execution and displays them at the end of the session:: # content of test_show_warnings.py import warnings def api_v1(): warnings.warn(UserWarning("api v1, should use functions from v2")) return 1 def test_one(): assert api_v1() == 1 Running pytest now produces this output:: $ pytest test_show_warnings.py =========================== test session starts ============================ platform linux -- Python 3.x.y, pytest-3.x.y, py-1.x.y, pluggy-0.x.y rootdir: $REGENDOC_TMPDIR, inifile: collected 1 item test_show_warnings.py . [100%] ============================= warnings summary ============================= test_show_warnings.py::test_one $REGENDOC_TMPDIR/test_show_warnings.py:4: UserWarning: api v1, should use functions from v2 warnings.warn(UserWarning("api v1, should use functions from v2")) -- Docs: http://doc.pytest.org/en/latest/warnings.html =================== 1 passed, 1 warnings in 0.12 seconds =================== Pytest by default catches all warnings except for ``DeprecationWarning`` and ``PendingDeprecationWarning``. The ``-W`` flag can be passed to control which warnings will be displayed or even turn them into errors:: $ pytest -q test_show_warnings.py -W error::UserWarning F [100%] ================================= FAILURES ================================= _________________________________ test_one _________________________________ def test_one(): > assert api_v1() == 1 test_show_warnings.py:8: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ def api_v1(): > warnings.warn(UserWarning("api v1, should use functions from v2")) E UserWarning: api v1, should use functions from v2 test_show_warnings.py:4: UserWarning 1 failed in 0.12 seconds The same option can be set in the ``pytest.ini`` file using the ``filterwarnings`` ini option. For example, the configuration below will ignore all user warnings, but will transform all other warnings into errors. .. code-block:: ini [pytest] filterwarnings = error ignore::UserWarning When a warning matches more than one option in the list, the action for the last matching option is performed. Both ``-W`` command-line option and ``filterwarnings`` ini option are based on Python's own `-W option`_ and `warnings.simplefilter`_, so please refer to those sections in the Python documentation for other examples and advanced usage. .. _`filterwarnings`: ``@pytest.mark.filterwarnings`` ------------------------------- .. versionadded:: 3.2 You can use the ``@pytest.mark.filterwarnings`` to add warning filters to specific test items, allowing you to have finer control of which warnings should be captured at test, class or even module level: .. code-block:: python import warnings def api_v1(): warnings.warn(UserWarning("api v1, should use functions from v2")) return 1 @pytest.mark.filterwarnings('ignore:api v1') def test_one(): assert api_v1() == 1 Filters applied using a mark take precedence over filters passed on the command line or configured by the ``filterwarnings`` ini option. You may apply a filter to all tests of a class by using the ``filterwarnings`` mark as a class decorator or to all tests in a module by setting the ``pytestmark`` variable: .. code-block:: python # turns all warnings into errors for this module pytestmark = pytest.mark.filterwarnings('error') .. note:: Except for these features, pytest does not change the python warning filter; it only captures and displays the warnings which are issued with respect to the currently configured filter, including changes to the filter made by test functions or by the system under test. .. note:: ``DeprecationWarning`` and ``PendingDeprecationWarning`` are hidden by the standard library by default so you have to explicitly configure them to be displayed in your ``pytest.ini``: .. code-block:: ini [pytest] filterwarnings = once::DeprecationWarning once::PendingDeprecationWarning *Credits go to Florian Schulze for the reference implementation in the* `pytest-warnings`_ *plugin.* .. _`-W option`: https://docs.python.org/3/using/cmdline.html?highlight=#cmdoption-W .. _warnings.simplefilter: https://docs.python.org/3/library/warnings.html#warnings.simplefilter .. _`pytest-warnings`: https://github.com/fschulze/pytest-warnings Disabling warning capture ------------------------- This feature is enabled by default but can be disabled entirely in your ``pytest.ini`` file with: .. code-block:: ini [pytest] addopts = -p no:warnings Or passing ``-p no:warnings`` in the command-line. .. _`asserting warnings`: .. _assertwarnings: .. _`asserting warnings with the warns function`: .. _warns: Asserting warnings with the warns function ----------------------------------------------- .. versionadded:: 2.8 You can check that code raises a particular warning using ``pytest.warns``, which works in a similar manner to :ref:`raises `:: import warnings import pytest def test_warning(): with pytest.warns(UserWarning): warnings.warn("my warning", UserWarning) The test will fail if the warning in question is not raised. The keyword argument ``match`` to assert that the exception matches a text or regex:: >>> with warns(UserWarning, match='must be 0 or None'): ... warnings.warn("value must be 0 or None", UserWarning) >>> with warns(UserWarning, match=r'must be \d+$'): ... warnings.warn("value must be 42", UserWarning) >>> with warns(UserWarning, match=r'must be \d+$'): ... warnings.warn("this is not here", UserWarning) Traceback (most recent call last): ... Failed: DID NOT WARN. No warnings of type ...UserWarning... was emitted... You can also call ``pytest.warns`` on a function or code string:: pytest.warns(expected_warning, func, *args, **kwargs) pytest.warns(expected_warning, "func(*args, **kwargs)") The function also returns a list of all raised warnings (as ``warnings.WarningMessage`` objects), which you can query for additional information:: with pytest.warns(RuntimeWarning) as record: warnings.warn("another warning", RuntimeWarning) # check that only one warning was raised assert len(record) == 1 # check that the message matches assert record[0].message.args[0] == "another warning" Alternatively, you can examine raised warnings in detail using the :ref:`recwarn ` fixture (see below). .. note:: ``DeprecationWarning`` and ``PendingDeprecationWarning`` are treated differently; see :ref:`ensuring_function_triggers`. .. _`recording warnings`: .. _recwarn: Recording warnings ------------------------ You can record raised warnings either using ``pytest.warns`` or with the ``recwarn`` fixture. To record with ``pytest.warns`` without asserting anything about the warnings, pass ``None`` as the expected warning type:: with pytest.warns(None) as record: warnings.warn("user", UserWarning) warnings.warn("runtime", RuntimeWarning) assert len(record) == 2 assert str(record[0].message) == "user" assert str(record[1].message) == "runtime" The ``recwarn`` fixture will record warnings for the whole function:: import warnings def test_hello(recwarn): warnings.warn("hello", UserWarning) assert len(recwarn) == 1 w = recwarn.pop(UserWarning) assert issubclass(w.category, UserWarning) assert str(w.message) == "hello" assert w.filename assert w.lineno Both ``recwarn`` and ``pytest.warns`` return the same interface for recorded warnings: a WarningsRecorder instance. To view the recorded warnings, you can iterate over this instance, call ``len`` on it to get the number of recorded warnings, or index into it to get a particular recorded warning. .. currentmodule:: _pytest.warnings Full API: :class:`WarningsRecorder`. .. _`ensuring a function triggers a deprecation warning`: .. _ensuring_function_triggers: Ensuring a function triggers a deprecation warning ------------------------------------------------------- You can also call a global helper for checking that a certain function call triggers a ``DeprecationWarning`` or ``PendingDeprecationWarning``:: import pytest def test_global(): pytest.deprecated_call(myfunction, 17) By default, ``DeprecationWarning`` and ``PendingDeprecationWarning`` will not be caught when using ``pytest.warns`` or ``recwarn`` because default Python warnings filters hide them. If you wish to record them in your own code, use the command ``warnings.simplefilter('always')``:: import warnings import pytest def test_deprecation(recwarn): warnings.simplefilter('always') warnings.warn("deprecated", DeprecationWarning) assert len(recwarn) == 1 assert recwarn.pop(DeprecationWarning) You can also use it as a contextmanager:: def test_global(): with pytest.deprecated_call(): myobject.deprecated_method()