208 lines
7.1 KiB
ReStructuredText
208 lines
7.1 KiB
ReStructuredText
Installation and Getting Started
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===================================
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**Pythons**: Python 3.5, 3.6, 3.7, PyPy3
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**Platforms**: Linux and Windows
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**PyPI package name**: `pytest <https://pypi.org/project/pytest/>`_
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**Documentation as PDF**: `download latest <https://media.readthedocs.org/pdf/pytest/latest/pytest.pdf>`_
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``pytest`` is a framework that makes building simple and scalable tests easy. Tests are expressive and readable—no boilerplate code required. Get started in minutes with a small unit test or complex functional test for your application or library.
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.. _`getstarted`:
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.. _`installation`:
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Install ``pytest``
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----------------------------------------
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1. Run the following command in your command line:
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.. code-block:: bash
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pip install -U pytest
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2. Check that you installed the correct version:
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.. code-block:: bash
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$ pytest --version
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This is pytest version 5.x.y, imported from $PYTHON_PREFIX/lib/python3.6/site-packages/pytest/__init__.py
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.. _`simpletest`:
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Create your first test
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----------------------------------------------------------
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Create a simple test function with just four lines of code:
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.. code-block:: python
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# content of test_sample.py
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def func(x):
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return x + 1
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def test_answer():
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assert func(3) == 5
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That’s it. You can now execute the test function:
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.. code-block:: pytest
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$ pytest
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=========================== test session starts ============================
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platform linux -- Python 3.x.y, pytest-5.x.y, py-1.x.y, pluggy-0.x.y
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cachedir: $PYTHON_PREFIX/.pytest_cache
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rootdir: $REGENDOC_TMPDIR
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collected 1 item
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test_sample.py F [100%]
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================================= FAILURES =================================
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_______________________________ test_answer ________________________________
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def test_answer():
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> assert func(3) == 5
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E assert 4 == 5
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E + where 4 = func(3)
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test_sample.py:6: AssertionError
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============================ 1 failed in 0.12s =============================
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This test returns a failure report because ``func(3)`` does not return ``5``.
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.. note::
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You can use the ``assert`` statement to verify test expectations. pytest’s `Advanced assertion introspection <http://docs.python.org/reference/simple_stmts.html#the-assert-statement>`_ will intelligently report intermediate values of the assert expression so you can avoid the many names `of JUnit legacy methods <http://docs.python.org/library/unittest.html#test-cases>`_.
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Run multiple tests
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----------------------------------------------------------
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``pytest`` will run all files of the form test_*.py or \*_test.py in the current directory and its subdirectories. More generally, it follows :ref:`standard test discovery rules <test discovery>`.
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Assert that a certain exception is raised
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--------------------------------------------------------------
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Use the :ref:`raises <assertraises>` helper to assert that some code raises an exception:
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.. code-block:: python
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# content of test_sysexit.py
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import pytest
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def f():
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raise SystemExit(1)
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def test_mytest():
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with pytest.raises(SystemExit):
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f()
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Execute the test function with “quiet” reporting mode:
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.. code-block:: pytest
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$ pytest -q test_sysexit.py
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. [100%]
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1 passed in 0.12s
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Group multiple tests in a class
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--------------------------------------------------------------
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Once you develop multiple tests, you may want to group them into a class. pytest makes it easy to create a class containing more than one test:
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.. code-block:: python
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# content of test_class.py
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class TestClass:
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def test_one(self):
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x = "this"
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assert "h" in x
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def test_two(self):
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x = "hello"
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assert hasattr(x, "check")
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``pytest`` discovers all tests following its :ref:`Conventions for Python test discovery <test discovery>`, so it finds both ``test_`` prefixed functions. There is no need to subclass anything, but make sure to prefix your class with ``Test`` otherwise the class will be skipped. We can simply run the module by passing its filename:
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.. code-block:: pytest
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$ pytest -q test_class.py
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.F [100%]
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================================= FAILURES =================================
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____________________________ TestClass.test_two ____________________________
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self = <test_class.TestClass object at 0xdeadbeef>
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def test_two(self):
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x = "hello"
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> assert hasattr(x, "check")
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E AssertionError: assert False
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E + where False = hasattr('hello', 'check')
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test_class.py:8: AssertionError
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1 failed, 1 passed in 0.12s
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The first test passed and the second failed. You can easily see the intermediate values in the assertion to help you understand the reason for the failure.
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Request a unique temporary directory for functional tests
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--------------------------------------------------------------
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``pytest`` provides `Builtin fixtures/function arguments <https://docs.pytest.org/en/latest/builtin.html>`_ to request arbitrary resources, like a unique temporary directory:
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.. code-block:: python
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# content of test_tmpdir.py
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def test_needsfiles(tmpdir):
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print(tmpdir)
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assert 0
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List the name ``tmpdir`` in the test function signature and ``pytest`` will lookup and call a fixture factory to create the resource before performing the test function call. Before the test runs, ``pytest`` creates a unique-per-test-invocation temporary directory:
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.. code-block:: pytest
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$ pytest -q test_tmpdir.py
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F [100%]
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================================= FAILURES =================================
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_____________________________ test_needsfiles ______________________________
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tmpdir = local('PYTEST_TMPDIR/test_needsfiles0')
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def test_needsfiles(tmpdir):
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print(tmpdir)
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> assert 0
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E assert 0
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test_tmpdir.py:3: AssertionError
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--------------------------- Captured stdout call ---------------------------
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PYTEST_TMPDIR/test_needsfiles0
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1 failed in 0.12s
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More info on tmpdir handling is available at :ref:`Temporary directories and files <tmpdir handling>`.
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Find out what kind of builtin :ref:`pytest fixtures <fixtures>` exist with the command:
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.. code-block:: bash
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pytest --fixtures # shows builtin and custom fixtures
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Note that this command omits fixtures with leading ``_`` unless the ``-v`` option is added.
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Continue reading
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-------------------------------------
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Check out additional pytest resources to help you customize tests for your unique workflow:
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* ":ref:`cmdline`" for command line invocation examples
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* ":ref:`existingtestsuite`" for working with pre-existing tests
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* ":ref:`mark`" for information on the ``pytest.mark`` mechanism
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* ":ref:`fixtures`" for providing a functional baseline to your tests
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* ":ref:`plugins`" for managing and writing plugins
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* ":ref:`goodpractices`" for virtualenv and test layouts
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.. include:: links.inc
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