.. _`noseintegration`:

How to run tests written for nose
=======================================

``pytest`` has basic support for running tests written for nose_.

.. warning::
    This functionality has been deprecated and is likely to be removed in ``pytest 8.x``.

.. _nosestyle:

Usage
-------------

After :ref:`installation` type:

.. code-block:: bash

    python setup.py develop  # make sure tests can import our package
    pytest  # instead of 'nosetests'

and you should be able to run your nose style tests and
make use of pytest's capabilities.

Supported nose Idioms
----------------------

* ``setup()`` and ``teardown()`` at module/class/method level: any function or method called ``setup`` will be called during the setup phase for each test, same for ``teardown``.
* ``SkipTest`` exceptions and markers
* setup/teardown decorators
* ``__test__`` attribute on modules/classes/functions
* general usage of nose utilities

Unsupported idioms / known issues
----------------------------------

- unittest-style ``setUp, tearDown, setUpClass, tearDownClass``
  are recognized only on ``unittest.TestCase`` classes but not
  on plain classes.  ``nose`` supports these methods also on plain
  classes but pytest deliberately does not.  As nose and pytest already
  both support ``setup_class, teardown_class, setup_method, teardown_method``
  it doesn't seem useful to duplicate the unittest-API like nose does.
  If you however rather think pytest should support the unittest-spelling on
  plain classes please post to :issue:`377`.

- nose imports test modules with the same import path (e.g.
  ``tests.test_mode``) but different file system paths
  (e.g. ``tests/test_mode.py`` and ``other/tests/test_mode.py``)
  by extending sys.path/import semantics.   pytest does not do that.  Note that
  `nose2 choose to avoid this sys.path/import hackery <https://nose2.readthedocs.io/en/latest/differences.html#test-discovery-and-loading>`_.

  If you place a conftest.py file in the root directory of your project
  (as determined by pytest) pytest will run tests "nose style" against
  the code below that directory by adding it to your ``sys.path`` instead of
  running against your installed code.

  You may find yourself wanting to do this if you ran ``python setup.py install``
  to set up your project, as opposed to ``python setup.py develop`` or any of
  the package manager equivalents.  Installing with develop in a
  virtual environment like tox is recommended over this pattern.

- nose-style doctests are not collected and executed correctly,
  also doctest fixtures don't work.

- no nose-configuration is recognized.

- ``yield``-based methods are
  fundamentally incompatible with pytest because they don't support fixtures
  properly since collection and test execution are separated.

Here is a table comparing the default supported naming conventions for both
nose and pytest.

========= ========================== ======= =====
what      default naming convention  pytest  nose
========= ========================== ======= =====
module    ``test*.py``                       ✅
module    ``test_*.py``              ✅       ✅
module    ``*_test.py``              ✅
module    ``*_tests.py``
class     ``*(unittest.TestCase)``   ✅       ✅
method    ``test_*``                 ✅       ✅
class     ``Test*``                  ✅
method    ``test_*``                 ✅
function  ``test_*``                 ✅
========= ========================== ======= =====


Migrating from nose to pytest
------------------------------

`nose2pytest <https://github.com/pytest-dev/nose2pytest>`_ is a Python script
and pytest plugin to help convert Nose-based tests into pytest-based tests.
Specifically, the script transforms ``nose.tools.assert_*`` function calls into
raw assert statements, while preserving format of original arguments
as much as possible.

.. _nose: https://nose.readthedocs.io/en/latest/
