test_ok2/doc/skipping.txt

skip and xfail mechanisms
=====================================================================

You can mark test functions for a conditional *skip* or as *xfail*,
expected-to-fail.  Skipping a test avoids running a test.
Whereas an xfail-marked test usually is run but if it fails it is
not reported in detail and counted separately. The latter allows
to keep track of real implementation problems whereas test skips
are normally tied to a condition, such as a platform or dependency
requirement without which considering or running the test does
not make sense.  If a test fails under all conditions then it's
probably best to mark your test as 'xfail'.

By running ``py.test -rxs`` you will see extra reporting 
information on skips and xfail-run tests at the end of a test run.

.. _skipif:

Skipping a single function
-------------------------------------------

Here is an example for marking a test function to be skipped
when run on a Python3 interpreter::

    @py.test.mark.skipif("sys.version_info >= (3,0)")
    def test_function():
        ...

During test function setup the skipif condition is
evaluated by calling ``eval(expr, namespace)``.  The namespace
contains the  ``sys`` and ``os`` modules and the test
``config`` object.  The latter allows you to skip based
on a test configuration value e.g. like this::

    @py.test.mark.skipif("not config.getvalue('db')")
    def test_function(...):
        ...

Create a shortcut for your conditional skip decorator
at module level like this::

    win32only = py.test.mark.skipif("sys.platform != 'win32'")

    @win32only
    def test_function():
        ...


skip groups of test functions
--------------------------------------

As with all function :ref:`marking` you can do it at
`whole class- or module level`_.  Here is an example
for skipping all methods of a test class based on platform::

    class TestPosixCalls:
        pytestmark = py.test.mark.skipif("sys.platform == 'win32'")

        def test_function(self):
            # will not be setup or run under 'win32' platform
            #

The ``pytestmark`` decorator will be applied to each test function.
If your code targets python2.6 or above you can equivalently use
the skipif decorator on classes::

    @py.test.mark.skipif("sys.platform == 'win32'")
    class TestPosixCalls:

        def test_function(self):
            # will not be setup or run under 'win32' platform
            #

It is fine in general to apply multiple "skipif" decorators
on a single function - this means that if any of the conditions
apply the function will be skipped.

.. _`whole class- or module level`: mark.html#scoped-marking

.. _xfail:

mark a test function as expected to fail
-------------------------------------------------------

You can use the ``xfail`` marker to indicate that you
expect the test to fail::

    @py.test.mark.xfail
    def test_function():
        ...

This test will be run but no traceback will be reported
when it fails. Instead terminal reporting will list it in the
"expected to fail" or "unexpectedly passing" sections.

Same as with skipif_ you can also selectively expect a failure
depending on platform::

    @py.test.mark.xfail("sys.version_info >= (3,0)")
    def test_function():
        ...

To not run a test and still regard it as "xfailed"::

    @py.test.mark.xfail(..., run=False)

To specify an explicit reason to be shown with xfailure detail::

    @py.test.mark.xfail(..., reason="my reason")

By specifying on the commandline::

    py.test --runxfail

you can force the running and reporting of a runnable ``xfail`` marked test.

imperative xfail from within a test or setup function
------------------------------------------------------

If you cannot declare xfail-conditions at import time
you can also imperatively produce an XFail-outcome from
within test or setup code.  Example::

    def test_function():
        if not valid_config():
            py.test.xfail("unsuppored configuration")


skipping on a missing import dependency
--------------------------------------------------

You can use the following import helper at module level
or within a test or test setup function::

    docutils = py.test.importorskip("docutils")

If ``docutils`` cannot be imported here, this will lead to a
skip outcome of the test.  You can also skip dependeing if
if a library does not come with a high enough version::

    docutils = py.test.importorskip("docutils", minversion="0.3")

The version will be read from the specified module's ``__version__`` attribute.

imperative skip from within a test or setup function
------------------------------------------------------

If for some reason you cannot declare skip-conditions
you can also imperatively produce a Skip-outcome from
within test or setup code.  Example::

    def test_function():
        if not valid_config():
            py.test.skip("unsuppored configuration")