240 lines
7.6 KiB
ReStructuredText
240 lines
7.6 KiB
ReStructuredText
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.. _`test generators`:
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.. _`parametrizing-tests`:
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.. _`parametrized test functions`:
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.. _`parametrize`:
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.. _`parametrize-basics`:
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Parametrizing fixtures and test functions
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==========================================================================
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pytest supports test parametrization in several well-integrated ways:
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- :py:func:`pytest.fixture` allows to define :ref:`parametrization
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at the level of fixture functions <fixture-parametrize>`.
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* `@pytest.mark.parametrize`_ allows to define parametrization at the
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function or class level, provides multiple argument/fixture sets
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for a particular test function or class.
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* `pytest_generate_tests`_ enables implementing your own custom
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dynamic parametrization scheme or extensions.
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.. _parametrizemark:
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.. _`@pytest.mark.parametrize`:
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``@pytest.mark.parametrize``: parametrizing test functions
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---------------------------------------------------------------------
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.. regendoc: wipe
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.. versionadded:: 2.2
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.. versionchanged:: 2.4
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Several improvements.
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The builtin ``pytest.mark.parametrize`` decorator enables
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parametrization of arguments for a test function. Here is a typical example
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of a test function that implements checking that a certain input leads
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to an expected output::
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# content of test_expectation.py
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import pytest
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@pytest.mark.parametrize("test_input,expected", [
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("3+5", 8),
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("2+4", 6),
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("6*9", 42),
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])
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def test_eval(test_input, expected):
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assert eval(test_input) == expected
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Here, the ``@parametrize`` decorator defines three different ``(test_input,expected)``
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tuples so that the ``test_eval`` function will run three times using
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them in turn::
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$ pytest
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======= test session starts ========
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platform linux -- Python 3.5.2, pytest-3.0.3, py-1.4.31, pluggy-0.4.0
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rootdir: $REGENDOC_TMPDIR, inifile:
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collected 3 items
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test_expectation.py ..F
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======= FAILURES ========
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_______ test_eval[6*9-42] ________
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test_input = '6*9', expected = 42
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@pytest.mark.parametrize("test_input,expected", [
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("3+5", 8),
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("2+4", 6),
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("6*9", 42),
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])
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def test_eval(test_input, expected):
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> assert eval(test_input) == expected
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E assert 54 == 42
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E + where 54 = eval('6*9')
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test_expectation.py:8: AssertionError
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======= 1 failed, 2 passed in 0.12 seconds ========
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As designed in this example, only one pair of input/output values fails
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the simple test function. And as usual with test function arguments,
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you can see the ``input`` and ``output`` values in the traceback.
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Note that you could also use the parametrize marker on a class or a module
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(see :ref:`mark`) which would invoke several functions with the argument sets.
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It is also possible to mark individual test instances within parametrize,
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for example with the builtin ``mark.xfail``::
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# content of test_expectation.py
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import pytest
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@pytest.mark.parametrize("test_input,expected", [
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("3+5", 8),
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("2+4", 6),
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pytest.param("6*9", 42,
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marks=pytest.mark.xfail),
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])
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def test_eval(test_input, expected):
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assert eval(test_input) == expected
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.. note::
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prior to version 3.1 the supported mechanism for marking values
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used the syntax::
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import pytest
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@pytest.mark.parametrize("test_input,expected", [
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("3+5", 8),
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("2+4", 6),
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pytest.mark.xfail(("6*9", 42),),
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])
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def test_eval(test_input, expected):
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assert eval(test_input) == expected
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This was an initial hack to support the feature but soon was demonstrated to be incomplete,
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broken for passing functions or applying multiple marks with the same name but different parameters.
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The old syntax will be removed in pytest-4.0.
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Let's run this::
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$ pytest
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======= test session starts ========
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platform linux -- Python 3.5.2, pytest-3.0.3, py-1.4.31, pluggy-0.4.0
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rootdir: $REGENDOC_TMPDIR, inifile:
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collected 3 items
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test_expectation.py ..x
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======= 2 passed, 1 xfailed in 0.12 seconds ========
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The one parameter set which caused a failure previously now
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shows up as an "xfailed (expected to fail)" test.
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To get all combinations of multiple parametrized arguments you can stack
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``parametrize`` decorators::
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import pytest
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@pytest.mark.parametrize("x", [0, 1])
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@pytest.mark.parametrize("y", [2, 3])
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def test_foo(x, y):
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pass
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This will run the test with the arguments set to x=0/y=2, x=0/y=3, x=1/y=2 and
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x=1/y=3.
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.. note::
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In versions prior to 2.4 one needed to specify the argument
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names as a tuple. This remains valid but the simpler ``"name1,name2,..."``
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comma-separated-string syntax is now advertised first because
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it's easier to write and produces less line noise.
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.. _`pytest_generate_tests`:
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Basic ``pytest_generate_tests`` example
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---------------------------------------------
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Sometimes you may want to implement your own parametrization scheme
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or implement some dynamism for determining the parameters or scope
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of a fixture. For this, you can use the ``pytest_generate_tests`` hook
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which is called when collecting a test function. Through the passed in
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``metafunc`` object you can inspect the requesting test context and, most
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importantly, you can call ``metafunc.parametrize()`` to cause
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parametrization.
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For example, let's say we want to run a test taking string inputs which
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we want to set via a new ``pytest`` command line option. Let's first write
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a simple test accepting a ``stringinput`` fixture function argument::
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# content of test_strings.py
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def test_valid_string(stringinput):
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assert stringinput.isalpha()
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Now we add a ``conftest.py`` file containing the addition of a
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command line option and the parametrization of our test function::
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# content of conftest.py
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def pytest_addoption(parser):
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parser.addoption("--stringinput", action="append", default=[],
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help="list of stringinputs to pass to test functions")
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def pytest_generate_tests(metafunc):
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if 'stringinput' in metafunc.fixturenames:
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metafunc.parametrize("stringinput",
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metafunc.config.option.stringinput)
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If we now pass two stringinput values, our test will run twice::
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$ pytest -q --stringinput="hello" --stringinput="world" test_strings.py
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..
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2 passed in 0.12 seconds
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Let's also run with a stringinput that will lead to a failing test::
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$ pytest -q --stringinput="!" test_strings.py
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F
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======= FAILURES ========
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_______ test_valid_string[!] ________
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stringinput = '!'
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def test_valid_string(stringinput):
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> assert stringinput.isalpha()
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E assert False
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E + where False = <built-in method isalpha of str object at 0xdeadbeef>()
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E + where <built-in method isalpha of str object at 0xdeadbeef> = '!'.isalpha
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test_strings.py:3: AssertionError
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1 failed in 0.12 seconds
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As expected our test function fails.
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If you don't specify a stringinput it will be skipped because
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``metafunc.parametrize()`` will be called with an empty parameter
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list::
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$ pytest -q -rs test_strings.py
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s
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======= short test summary info ========
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SKIP [1] test_strings.py:1: got empty parameter set ['stringinput'], function test_valid_string at $REGENDOC_TMPDIR/test_strings.py:1
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1 skipped in 0.12 seconds
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For further examples, you might want to look at :ref:`more
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parametrization examples <paramexamples>`.
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.. _`metafunc object`:
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The **metafunc** object
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-------------------------------------------
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.. currentmodule:: _pytest.python
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.. autoclass:: Metafunc
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:members:
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