159 lines
5.0 KiB
ReStructuredText
159 lines
5.0 KiB
ReStructuredText
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.. _`tmp_path handling`:
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.. _tmp_path:
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How to use temporary directories and files in tests
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===================================================
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The ``tmp_path`` fixture
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------------------------
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You can use the ``tmp_path`` fixture which will
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provide a temporary directory unique to the test invocation,
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created in the `base temporary directory`_.
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``tmp_path`` is a :class:`pathlib.Path` object. Here is an example test usage:
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.. code-block:: python
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# content of test_tmp_path.py
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CONTENT = "content"
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def test_create_file(tmp_path):
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d = tmp_path / "sub"
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d.mkdir()
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p = d / "hello.txt"
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p.write_text(CONTENT)
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assert p.read_text() == CONTENT
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assert len(list(tmp_path.iterdir())) == 1
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assert 0
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Running this would result in a passed test except for the last
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``assert 0`` line which we use to look at values:
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.. code-block:: pytest
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$ pytest test_tmp_path.py
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=========================== test session starts ============================
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platform linux -- Python 3.x.y, pytest-7.x.y, pluggy-1.x.y
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rootdir: /home/sweet/project
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collected 1 item
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test_tmp_path.py F [100%]
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================================= FAILURES =================================
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_____________________________ test_create_file _____________________________
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tmp_path = PosixPath('PYTEST_TMPDIR/test_create_file0')
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def test_create_file(tmp_path):
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d = tmp_path / "sub"
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d.mkdir()
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p = d / "hello.txt"
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p.write_text(CONTENT)
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assert p.read_text() == CONTENT
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assert len(list(tmp_path.iterdir())) == 1
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> assert 0
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E assert 0
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test_tmp_path.py:11: AssertionError
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========================= short test summary info ==========================
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FAILED test_tmp_path.py::test_create_file - assert 0
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============================ 1 failed in 0.12s =============================
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.. _`tmp_path_factory example`:
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The ``tmp_path_factory`` fixture
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--------------------------------
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The ``tmp_path_factory`` is a session-scoped fixture which can be used
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to create arbitrary temporary directories from any other fixture or test.
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For example, suppose your test suite needs a large image on disk, which is
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generated procedurally. Instead of computing the same image for each test
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that uses it into its own ``tmp_path``, you can generate it once per-session
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to save time:
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.. code-block:: python
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# contents of conftest.py
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import pytest
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@pytest.fixture(scope="session")
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def image_file(tmp_path_factory):
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img = compute_expensive_image()
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fn = tmp_path_factory.mktemp("data") / "img.png"
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img.save(fn)
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return fn
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# contents of test_image.py
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def test_histogram(image_file):
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img = load_image(image_file)
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# compute and test histogram
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See :ref:`tmp_path_factory API <tmp_path_factory factory api>` for details.
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.. _`tmpdir and tmpdir_factory`:
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.. _tmpdir:
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The ``tmpdir`` and ``tmpdir_factory`` fixtures
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---------------------------------------------------
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The ``tmpdir`` and ``tmpdir_factory`` fixtures are similar to ``tmp_path``
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and ``tmp_path_factory``, but use/return legacy `py.path.local`_ objects
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rather than standard :class:`pathlib.Path` objects.
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.. note::
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These days, it is preferred to use ``tmp_path`` and ``tmp_path_factory``.
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In order to help modernize old code bases, one can run pytest with the legacypath
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plugin disabled:
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.. code-block:: bash
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pytest -p no:legacypath
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This will trigger errors on tests using the legacy paths.
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It can also be permanently set as part of the :confval:`addopts` parameter in the
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config file.
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See :fixture:`tmpdir <tmpdir>` :fixture:`tmpdir_factory <tmpdir_factory>`
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API for details.
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.. _`base temporary directory`:
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The default base temporary directory
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-----------------------------------------------
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Temporary directories are by default created as sub-directories of
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the system temporary directory. The base name will be ``pytest-NUM`` where
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``NUM`` will be incremented with each test run.
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By default, entries older than 3 temporary directories will be removed.
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This behavior can be configured with :confval:`tmp_path_retention_count` and
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:confval:`tmp_path_retention_policy`.
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Using the ``--basetemp``
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option will remove the directory before every run, effectively meaning the temporary directories
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of only the most recent run will be kept.
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You can override the default temporary directory setting like this:
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.. code-block:: bash
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pytest --basetemp=mydir
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.. warning::
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The contents of ``mydir`` will be completely removed, so make sure to use a directory
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for that purpose only.
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When distributing tests on the local machine using ``pytest-xdist``, care is taken to
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automatically configure a basetemp directory for the sub processes such that all temporary
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data lands below a single per-test run basetemp directory.
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.. _`py.path.local`: https://py.readthedocs.io/en/latest/path.html
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