test_ok1/doc/en/parametrize.rst

.. _`test generators`:
.. _`parametrizing-tests`:
.. _`parametrized test functions`:
.. _`parametrize`:

.. _`parametrize-basics`:

Parametrizing fixtures and test functions
==========================================================================

pytest enables test parametrization at several levels:

- :py:func:`pytest.fixture` allows one to :ref:`parametrize fixture 
  functions <fixture-parametrize>`.

* `@pytest.mark.parametrize`_ allows one to define multiple sets of 
  arguments and fixtures at the test function or class.

* `pytest_generate_tests`_ allows one to define custom parametrization 
  schemes or extensions.

.. _parametrizemark:
.. _`@pytest.mark.parametrize`:


``@pytest.mark.parametrize``: parametrizing test functions
---------------------------------------------------------------------

.. regendoc: wipe

.. versionadded:: 2.2
.. versionchanged:: 2.4
    Several improvements.

The builtin ``pytest.mark.parametrize`` decorator enables
parametrization of arguments for a test function.  Here is a typical example
of a test function that implements checking that a certain input leads
to an expected output::

    # content of test_expectation.py
    import pytest
    @pytest.mark.parametrize("test_input,expected", [
        ("3+5", 8),
        ("2+4", 6),
        ("6*9", 42),
    ])
    def test_eval(test_input, expected):
        assert eval(test_input) == expected

Here, the ``@parametrize`` decorator defines three different ``(test_input,expected)``
tuples so that the ``test_eval`` function will run three times using
them in turn::

    $ pytest
    ======= 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 3 items
    
    test_expectation.py ..F
    
    ======= FAILURES ========
    _______ test_eval[6*9-42] ________
    
    test_input = '6*9', expected = 42
    
        @pytest.mark.parametrize("test_input,expected", [
            ("3+5", 8),
            ("2+4", 6),
            ("6*9", 42),
        ])
        def test_eval(test_input, expected):
    >       assert eval(test_input) == expected
    E       AssertionError: assert 54 == 42
    E        +  where 54 = eval('6*9')
    
    test_expectation.py:8: AssertionError
    ======= 1 failed, 2 passed in 0.12 seconds ========

As designed in this example, only one pair of input/output values fails
the simple test function.  And as usual with test function arguments,
you can see the ``input`` and ``output`` values in the traceback.

Note that you could also use the parametrize marker on a class or a module
(see :ref:`mark`) which would invoke several functions with the argument sets.

It is also possible to mark individual test instances within parametrize,
for example with the builtin ``mark.xfail``::

    # content of test_expectation.py
    import pytest
    @pytest.mark.parametrize("test_input,expected", [
        ("3+5", 8),
        ("2+4", 6),
        pytest.param("6*9", 42,
                     marks=pytest.mark.xfail),
    ])
    def test_eval(test_input, expected):
        assert eval(test_input) == expected

.. note::

  prior to version 3.1 the supported mechanism for marking values
  used the syntax::

        import pytest
        @pytest.mark.parametrize("test_input,expected", [
            ("3+5", 8),
            ("2+4", 6),
            pytest.mark.xfail(("6*9", 42),),
        ])
        def test_eval(test_input, expected):
            assert eval(test_input) == expected


  This was an initial hack to support the feature but soon was demonstrated to be incomplete,
  broken for passing functions or applying multiple marks with the same name but different parameters.
  The old syntax will be removed in pytest-4.0.


Let's run this::

    $ pytest
    ======= 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 3 items
    
    test_expectation.py ..x
    
    ======= 2 passed, 1 xfailed in 0.12 seconds ========

The one parameter set which caused a failure previously now
shows up as an "xfailed (expected to fail)" test.

To get all combinations of multiple parametrized arguments you can stack
``parametrize`` decorators::

    import pytest
    @pytest.mark.parametrize("x", [0, 1])
    @pytest.mark.parametrize("y", [2, 3])
    def test_foo(x, y):
        pass

This will run the test with the arguments set to x=0/y=2, x=0/y=3, x=1/y=2 and
x=1/y=3.

.. note::

    In versions prior to 2.4 one needed to specify the argument
    names as a tuple.  This remains valid but the simpler ``"name1,name2,..."``
    comma-separated-string syntax is now advertised first because
    it's easier to write and produces less line noise.

.. _`pytest_generate_tests`:

Basic ``pytest_generate_tests`` example
---------------------------------------------

Sometimes you may want to implement your own parametrization scheme
or implement some dynamism for determining the parameters or scope
of a fixture.   For this, you can use the ``pytest_generate_tests`` hook
which is called when collecting a test function.  Through the passed in
``metafunc`` object you can inspect the requesting test context and, most
importantly, you can call ``metafunc.parametrize()`` to cause
parametrization.

For example, let's say we want to run a test taking string inputs which
we want to set via a new ``pytest`` command line option.  Let's first write
a simple test accepting a ``stringinput`` fixture function argument::

    # content of test_strings.py

    def test_valid_string(stringinput):
        assert stringinput.isalpha()

Now we add a ``conftest.py`` file containing the addition of a
command line option and the parametrization of our test function::

    # content of conftest.py

    def pytest_addoption(parser):
        parser.addoption("--stringinput", action="append", default=[],
            help="list of stringinputs to pass to test functions")

    def pytest_generate_tests(metafunc):
        if 'stringinput' in metafunc.fixturenames:
            metafunc.parametrize("stringinput",
                                 metafunc.config.getoption('stringinput'))

If we now pass two stringinput values, our test will run twice::

    $ pytest -q --stringinput="hello" --stringinput="world" test_strings.py
    ..
    2 passed in 0.12 seconds

Let's also run with a stringinput that will lead to a failing test::

    $ pytest -q --stringinput="!" test_strings.py
    F
    ======= FAILURES ========
    _______ test_valid_string[!] ________
    
    stringinput = '!'
    
        def test_valid_string(stringinput):
    >       assert stringinput.isalpha()
    E       AssertionError: assert False
    E        +  where False = <built-in method isalpha of str object at 0xdeadbeef>()
    E        +    where <built-in method isalpha of str object at 0xdeadbeef> = '!'.isalpha
    
    test_strings.py:3: AssertionError
    1 failed in 0.12 seconds

As expected our test function fails.

If you don't specify a stringinput it will be skipped because
``metafunc.parametrize()`` will be called with an empty parameter
list::

    $ pytest -q -rs test_strings.py
    s
    ======= short test summary info ========
    SKIP [1] test_strings.py:1: got empty parameter set ['stringinput'], function test_valid_string at $REGENDOC_TMPDIR/test_strings.py:1
    1 skipped in 0.12 seconds

For further examples, you might want to look at :ref:`more
parametrization examples <paramexamples>`.

.. _`metafunc object`:

The **metafunc** object
-------------------------------------------

.. currentmodule:: _pytest.python
.. autoclass:: Metafunc
    :members: