test_ok1/doc/example/simple.txt

.. highlightlang:: python

basic patterns and examples
==========================================================

pass different values to a test function, depending on command line options
----------------------------------------------------------------------------

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Suppose we want to write a test that depends on a command line option.
Here is a basic pattern how to achieve this::

    # content of test_sample.py
    def test_answer(cmdopt):
        if cmdopt == "type1":
            print ("first")
        elif cmdopt == "type2":
            print ("second")
        assert 0 # to see what was printed


For this to work we need to add a command line option and
provide the ``cmdopt`` through a :ref:`function argument <funcarg>` factory::

    # content of conftest.py
    def pytest_addoption(parser):
        parser.addoption("--cmdopt", action="store", default="type1",
            help="my option: type1 or type2")

    def pytest_funcarg__cmdopt(request):
        return request.config.option.cmdopt

Let's run this without supplying our new command line option::

    $ py.test -q test_sample.py
    collecting ... collected 1 items
    F
    ================================= FAILURES =================================
    _______________________________ test_answer ________________________________
    
    cmdopt = 'type1'
    
        def test_answer(cmdopt):
            if cmdopt == "type1":
                print ("first")
            elif cmdopt == "type2":
                print ("second")
    >       assert 0 # to see what was printed
    E       assert 0
    
    test_sample.py:6: AssertionError
    ----------------------------- Captured stdout ------------------------------
    first
    1 failed in 0.02 seconds

And now with supplying a command line option::

    $ py.test -q --cmdopt=type2
    collecting ... collected 1 items
    F
    ================================= FAILURES =================================
    _______________________________ test_answer ________________________________
    
    cmdopt = 'type2'
    
        def test_answer(cmdopt):
            if cmdopt == "type1":
                print ("first")
            elif cmdopt == "type2":
                print ("second")
    >       assert 0 # to see what was printed
    E       assert 0
    
    test_sample.py:6: AssertionError
    ----------------------------- Captured stdout ------------------------------
    second
    1 failed in 0.02 seconds

Ok, this completes the basic pattern.  However, one often rather
wants to process command line options outside of the test and
rather pass in different or more complex objects.  See the
next example or refer to :ref:`mysetup` for more information
on real-life examples.

generating parameters combinations, depending on command line
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Let's say we want to execute a test with different parameters
and the parameter range shall be determined by a command
line argument.  Let's first write a simple computation test::

    # content of test_compute.py

    def test_compute(param1):
        assert param1 < 4

Now we add a test configuration like this::

    # content of conftest.py

    def pytest_addoption(parser):
        parser.addoption("--all", action="store_true",
            help="run all combinations")

    def pytest_generate_tests(metafunc):
        if 'param1' in metafunc.funcargnames:
            if metafunc.config.option.all:
                end = 5
            else:
                end = 2
            for i in range(end):
                metafunc.addcall(funcargs={'param1': i})

This means that we only run 2 tests if we do not pass ``--all``::

    $ py.test -q test_compute.py
    collecting ... collected 2 items
    ..
    2 passed in 0.01 seconds

We run only two computations, so we see two dots.
let's run the full monty::

    $ py.test -q --all
    collecting ... collected 5 items
    ....F
    ================================= FAILURES =================================
    _____________________________ test_compute[4] ______________________________
    
    param1 = 4
    
        def test_compute(param1):
    >       assert param1 < 4
    E       assert 4 < 4
    
    test_compute.py:3: AssertionError
    1 failed, 4 passed in 0.02 seconds

As expected when running the full range of ``param1`` values
we'll get an error on the last one.

dynamically adding command line options
--------------------------------------------------------------

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Through :confval:`addopts` you can statically add command line
options for your project.  You can also dynamically modify
the command line arguments before they get processed::

    # content of conftest.py
    import sys
    def pytest_cmdline_preparse(args):
        if 'xdist' in sys.modules: # pytest-xdist plugin
            import multiprocessing
            num = max(multiprocessing.cpu_count() / 2, 1)
            args[:] = ["-n", str(num)] + args

If you have the :ref:`xdist plugin <xdist>` installed
you will now always perform test runs using a number
of subprocesses close to your CPU. Running in an empty
directory with the above conftest.py::

    $ py.test
    =========================== test session starts ============================
    platform linux2 -- Python 2.6.5 -- pytest-2.0.1.dev3
    gw0 I / gw1 I / gw2 I / gw3 I
    gw0 [0] / gw1 [0] / gw2 [0] / gw3 [0]
    
    scheduling tests via LoadScheduling
    
    =============================  in 0.29 seconds =============================

.. _`retrieved by hooks as item keywords`:

control skipping of tests according to command line option
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Here is a ``conftest.py`` file adding a ``--runslow`` command
line option to control skipping of ``slow`` marked tests::

    # content of conftest.py

    import pytest
    def pytest_addoption(parser):
        parser.addoption("--runslow", action="store_true",
            help="run slow tests")

    def pytest_runtest_setup(item):
        if 'slow' in item.keywords and not item.config.getvalue("runslow"):
            pytest.skip("need --runslow option to run")

We can now write a test module like this::

    # content of test_module.py

    import pytest
    slow = pytest.mark.slow

    def test_func_fast():
        pass

    @slow
    def test_func_slow():
        pass

and when running it will see a skipped "slow" test::

    $ py.test -rs    # "-rs" means report details on the little 's'
    =========================== test session starts ============================
    platform linux2 -- Python 2.6.5 -- pytest-2.0.1.dev3
    collecting ... collected 2 items
    
    test_module.py .s
    ========================= short test summary info ==========================
    SKIP [1] /tmp/doc-exec-25/conftest.py:9: need --runslow option to run
    
    =================== 1 passed, 1 skipped in 0.02 seconds ====================

Or run it including the ``slow`` marked test::

    $ py.test --runslow
    =========================== test session starts ============================
    platform linux2 -- Python 2.6.5 -- pytest-2.0.1.dev3
    collecting ... collected 2 items
    
    test_module.py ..
    
    ========================= 2 passed in 0.01 seconds =========================

writing well integrated assertion helpers
--------------------------------------------------

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If you have a test helper function called from a test you can
use the ``pytest.fail`` marker to fail a test with a certain message.
The test support function will not show up in the traceback if you
set the ``__tracebackhide__`` option somewhere in the helper function.
Example::

    # content of test_checkconfig.py
    import pytest
    def checkconfig(x):
        __tracebackhide__ = True
        if not hasattr(x, "config"):
            pytest.fail("not configured: %s" %(x,))

    def test_something():
        checkconfig(42)

The ``__tracebackhide__`` setting influences py.test showing
of tracebacks: the ``checkconfig`` function will not be shown
unless the ``--fulltrace`` command line option is specified.
Let's run our little function::

    $ py.test -q test_checkconfig.py
    collecting ... collected 1 items
    F
    ================================= FAILURES =================================
    ______________________________ test_something ______________________________
    
        def test_something():
    >       checkconfig(42)
    E       Failed: not configured: 42
    
    test_checkconfig.py:8: Failed
    1 failed in 0.02 seconds

Detect if running from within a py.test run
--------------------------------------------------------------

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Usually it is a bad idea to make application code
behave differently if called from a test.  But if you
absolutely must find out if your application code is
running from a test you can do something like this::

    # content of conftest.py

    def pytest_configure(config):
        import sys
        sys._called_from_test = True

    def pytest_unconfigure(config):
        del sys._called_from_test

and then check for the ``sys._called_from_test`` flag::

    if hasattr(sys, '_called_from_test'):
        # called from within a test run
    else:
        # called "normally"
    
accordingly in your application.  It's also a good idea
to rather use your own application module rather than ``sys``
for handling flag.