Skip and xfail: dealing with tests that can not succeed

If you have test functions that cannot be run on certain platforms or that you expect to fail you can mark them accordingly or you may call helper functions during execution of setup or test functions.

A skip means that you expect your test to pass unless the environment (e.g. wrong Python interpreter, missing dependency) prevents it to run. And xfail means that your test can run but you expect it to fail because there is an implementation problem.

pytest counts and lists skip and xfail tests separately. Detailed information about skipped/xfailed tests is not shown by default to avoid cluttering the output. You can use the -r option to see details corresponding to the “short” letters shown in the test progress:

py.test -rxs  # show extra info on skips and xfails

(See How to change command line options defaults)

Marking a test function to be skipped

New in version 2.0,: 2.4

Here is an example of marking a test function to be skipped when run on a Python3.3 interpreter:

import sys
@pytest.mark.skipif(sys.version_info < (3,3),
                    reason="requires python3.3")
def test_function():
    ...

During test function setup the condition (“sys.version_info >= (3,3)”) is checked. If it evaluates to True, the test function will be skipped with the specified reason. Note that pytest enforces specifying a reason in order to report meaningful “skip reasons” (e.g. when using -rs). If the condition is a string, it will be evaluated as python expression.

You can share skipif markers between modules. Consider this test module:

# content of test_mymodule.py

import mymodule
minversion = pytest.mark.skipif(mymodule.__versioninfo__ < (1,1),
                                reason="at least mymodule-1.1 required")
@minversion
def test_function():
    ...

You can import it from another test module:

# test_myothermodule.py
from test_mymodule import minversion

@minversion
def test_anotherfunction():
    ...

For larger test suites it’s usually a good idea to have one file where you define the markers which you then consistently apply throughout your test suite.

Alternatively, the pre pytest-2.4 way to specify condition strings instead of booleans will remain fully supported in future versions of pytest. It couldn’t be easily used for importing markers between test modules so it’s no longer advertised as the primary method.

Skip all test functions of a class or module

As with all function marking you can skip test functions at the whole class- or module level. If your code targets python2.6 or above you use the skipif decorator (and any other marker) on classes:

@pytest.mark.skipif(sys.platform == 'win32',
                    reason="requires windows")
class TestPosixCalls:

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

If the condition is true, this marker will produce a skip result for each of the test methods.

If your code targets python2.5 where class-decorators are not available, you can set the pytestmark attribute of a class:

class TestPosixCalls:
    pytestmark = pytest.mark.skipif(sys.platform == 'win32',
                                    reason="requires Windows")

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

As with the class-decorator, the pytestmark special name tells pytest to apply it to each test function in the class.

If you want to skip all test functions of a module, you must use the pytestmark name on the global level:

# test_module.py

pytestmark = pytest.mark.skipif(...)

If multiple “skipif” decorators are applied to a test function, it will be skipped if any of the skip conditions is true.

Mark a test function as expected to fail

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

@pytest.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.

By specifying on the commandline:

pytest --runxfail

you can force the running and reporting of an xfail marked test as if it weren’t marked at all.

As with skipif you can also mark your expectation of a failure on a particular platform:

@pytest.mark.xfail(sys.version_info >= (3,3),
                   reason="python3.3 api changes")
def test_function():
    ...

If you want to be more specific as to why the test is failing, you can specify a single exception, or a list of exceptions, in the raises argument. Then the test will be reported as a regular failure if it fails with an exception not mentioned in raises.

You can furthermore prevent the running of an “xfail” test or specify a reason such as a bug ID or similar. Here is a simple test file with the several usages:

import pytest
xfail = pytest.mark.xfail

@xfail
def test_hello():
    assert 0

@xfail(run=False)
def test_hello2():
    assert 0

@xfail("hasattr(os, 'sep')")
def test_hello3():
    assert 0

@xfail(reason="bug 110")
def test_hello4():
    assert 0

@xfail('pytest.__version__[0] != "17"')
def test_hello5():
    assert 0

def test_hello6():
    pytest.xfail("reason")

@xfail(raises=IndexError)
def test_hello7():
    x = []
    x[1] = 1

Running it with the report-on-xfail option gives this output:

example $ py.test -rx xfail_demo.py
=========================== test session starts ============================
platform linux -- Python 3.4.0 -- py-1.4.25.dev2 -- pytest-2.6.3.dev3
collected 7 items

xfail_demo.py xxxxxxx
========================= short test summary info ==========================
XFAIL xfail_demo.py::test_hello
XFAIL xfail_demo.py::test_hello2
  reason: [NOTRUN]
XFAIL xfail_demo.py::test_hello3
  condition: hasattr(os, 'sep')
XFAIL xfail_demo.py::test_hello4
  bug 110
XFAIL xfail_demo.py::test_hello5
  condition: pytest.__version__[0] != "17"
XFAIL xfail_demo.py::test_hello6
  reason: reason
XFAIL xfail_demo.py::test_hello7

======================== 7 xfailed in 0.05 seconds =========================

Skip/xfail with parametrize

It is possible to apply markers like skip and xfail to individual test instances when using parametrize:

import pytest

@pytest.mark.parametrize(("n", "expected"), [
    (1, 2),
    pytest.mark.xfail((1, 0)),
    pytest.mark.xfail(reason="some bug")((1, 3)),
    (2, 3),
    (3, 4),
    (4, 5),
    pytest.mark.skipif("sys.version_info >= (3,0)")((10, 11)),
])
def test_increment(n, expected):
    assert n + 1 == expected

Imperative xfail from within a test or setup function

If you cannot declare xfail- of skipif conditions at import time you can also imperatively produce an according outcome imperatively, in test or setup code:

def test_function():
    if not valid_config():
        pytest.xfail("failing configuration (but should work)")
        # or
        pytest.skip("unsupported 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 = pytest.importorskip("docutils")

If docutils cannot be imported here, this will lead to a skip outcome of the test. You can also skip based on the version number of a library:

docutils = pytest.importorskip("docutils", minversion="0.3")

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

specifying conditions as strings versus booleans

Prior to pytest-2.4 the only way to specify skipif/xfail conditions was to use strings:

import sys
@pytest.mark.skipif("sys.version_info >= (3,3)")
def test_function():
    ...

During test function setup the skipif condition is evaluated by calling eval('sys.version_info >= (3,0)', namespace). The namespace contains all the module globals, and os and sys as a minimum.

Since pytest-2.4 condition booleans are considered preferable because markers can then be freely imported between test modules. With strings you need to import not only the marker but all variables everything used by the marker, which violates encapsulation.

The reason for specifying the condition as a string was that pytest can report a summary of skip conditions based purely on the condition string. With conditions as booleans you are required to specify a reason string.

Note that string conditions will remain fully supported and you are free to use them if you have no need for cross-importing markers.

The evaluation of a condition string in pytest.mark.skipif(conditionstring) or pytest.mark.xfail(conditionstring) takes place in a namespace dictionary which is constructed as follows:

  • the namespace is initialized by putting the sys and os modules and the pytest config object into it.
  • updated with the module globals of the test function for which the expression is applied.

The pytest config object allows you to skip based on a test configuration value which you might have added:

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

The equivalent with “boolean conditions” is:

@pytest.mark.skipif(not pytest.config.getvalue("db"),
                    reason="--db was not specified")
def test_function(...):
    pass

Note

You cannot use pytest.config.getvalue() in code imported before py.test’s argument parsing takes place. For example, conftest.py files are imported before command line parsing and thus config.getvalue() will not execute correctly.