Source

pytest / doc / example / simple.txt

Full commit

.. highlightlang:: python

Basic patterns and examples
==========================================================

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

.. regendoc:wipe

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 0.50 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.


Dynamically adding command line options
--------------------------------------------------------------

.. regendoc:wipe

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 darwin -- Python 2.7.1 -- pytest-2.2.2
    gw0 I
    gw0 [0]
    
    scheduling tests via LoadScheduling
    
    =============================  in 5.12 seconds =============================

.. _`excontrolskip`:

Control skipping of tests according to command line option
--------------------------------------------------------------

.. regendoc:wipe

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 darwin -- Python 2.7.1 -- pytest-2.2.2
    collecting ... collected 2 items
    
    test_module.py .s
    ========================= short test summary info ==========================
    SKIP [1] /Users/hpk/tmp/doc-exec-158/conftest.py:9: need --runslow option to run
    
    =================== 1 passed, 1 skipped in 0.09 seconds ====================

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

    $ py.test --runslow
    =========================== test session starts ============================
    platform darwin -- Python 2.7.1 -- pytest-2.2.2
    collecting ... collected 2 items
    
    test_module.py ..
    
    ========================= 2 passed in 0.02 seconds =========================

Writing well integrated assertion helpers
--------------------------------------------------

.. regendoc:wipe

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 0.07 seconds

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

.. regendoc:wipe

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 use your own application module rather than ``sys``
for handling flag.

Adding info to test report header
--------------------------------------------------------------

.. regendoc:wipe

It's easy to present extra information in a py.test run::

    # content of conftest.py
    
    def pytest_report_header(config):
        return "project deps: mylib-1.1"

which will add the string to the test header accordingly::

    $ py.test
    =========================== test session starts ============================
    platform darwin -- Python 2.7.1 -- pytest-2.2.2
    project deps: mylib-1.1
    collecting ... collected 0 items
    
    =============================  in 0.01 seconds =============================

.. regendoc:wipe

You can also return a list of strings which will be considered as several
lines of information.  You can of course also make the amount of reporting
information on e.g. the value of ``config.option.verbose`` so that
you present more information appropriately::

    # content of conftest.py

    def pytest_report_header(config):
        if config.option.verbose > 0:
            return ["info1: did you know that ...", "did you?"]

which will add info only when run with "--v"::

    $ py.test -v
    =========================== test session starts ============================
    platform darwin -- Python 2.7.1 -- pytest-2.2.2 -- /Users/hpk/venv/0/bin/python
    info1: did you know that ...
    did you?
    collecting ... collected 0 items
    
    =============================  in 0.03 seconds =============================

and nothing when run plainly::

    $ py.test
    =========================== test session starts ============================
    platform darwin -- Python 2.7.1 -- pytest-2.2.2
    collecting ... collected 0 items
    
    =============================  in 0.01 seconds =============================

profiling test duration
--------------------------

.. regendoc:wipe

.. versionadded: 2.2

If you have a slow running large test suite you might want to find
out which tests are the slowest. Let's make an artifical test suite::

    # content of test_some_are_slow.py

    import time

    def test_funcfast():
        pass

    def test_funcslow1():
        time.sleep(0.1)

    def test_funcslow2():
        time.sleep(0.2)

Now we can profile which test functions execute the slowest::

    $ py.test --durations=3
    =========================== test session starts ============================
    platform darwin -- Python 2.7.1 -- pytest-2.2.2
    collecting ... collected 3 items
    
    test_some_are_slow.py ...
    
    ========================= slowest 3 test durations =========================
    0.20s call     test_some_are_slow.py::test_funcslow2
    0.10s call     test_some_are_slow.py::test_funcslow1
    0.00s call     test_some_are_slow.py::test_funcfast
    ========================= 3 passed in 0.33 seconds =========================