Pytest-Working with custom markers

Here are some examples using the mark{.interpreted-text role=“ref”}
mechanism.

Marking test functions and selecting them for a run {#mark run}

You can “mark” a test function with custom metadata like this:

# content of test_server.py

import pytest


@pytest.mark.webtest
def test_send_http():
    pass  # perform some webtest test for your app


def test_something_quick():
    pass


def test_another():
    pass


class TestClass:
    def test_method(self):
        pass

You can then restrict a test run to only run tests marked with
webtest:

$ pytest -v -m webtest
platform linux -- Python 3.x.y, pytest-6.x.y, py-1.x.y, pluggy-0.x.y -- $PYTHON_PREFIX/bin/python
cachedir: $PYTHON_PREFIX/.pytest_cache
rootdir: $REGENDOC_TMPDIR
collecting ... collected 4 items / 3 deselected / 1 selected

test_server.py::test_send_http PASSED                                [100%]

Or the inverse, running all tests except the webtest ones:

$ pytest -v -m "not webtest"
platform linux -- Python 3.x.y, pytest-6.x.y, py-1.x.y, pluggy-0.x.y -- $PYTHON_PREFIX/bin/python
cachedir: $PYTHON_PREFIX/.pytest_cache
rootdir: $REGENDOC_TMPDIR
collecting ... collected 4 items / 1 deselected / 3 selected

test_server.py::test_something_quick PASSED                          [ 33%]
test_server.py::test_another PASSED                                  [ 66%]
test_server.py::TestClass::test_method PASSED                        [100%]

Selecting tests based on their node ID

You can provide one or more node IDs <node-id>{.interpreted-text
role=“ref”} as positional arguments to select only specified tests. This
makes it easy to select tests based on their module, class, method, or
function name:

$ pytest -v test_server.py::TestClass::test_method
platform linux -- Python 3.x.y, pytest-6.x.y, py-1.x.y, pluggy-0.x.y -- $PYTHON_PREFIX/bin/python
cachedir: $PYTHON_PREFIX/.pytest_cache
rootdir: $REGENDOC_TMPDIR
collecting ... collected 1 item

test_server.py::TestClass::test_method PASSED                        [100%]

You can also select on the class:

$ pytest -v test_server.py::TestClass
platform linux -- Python 3.x.y, pytest-6.x.y, py-1.x.y, pluggy-0.x.y -- $PYTHON_PREFIX/bin/python
cachedir: $PYTHON_PREFIX/.pytest_cache
rootdir: $REGENDOC_TMPDIR
collecting ... collected 1 item

test_server.py::TestClass::test_method PASSED                        [100%]

Or select multiple nodes:

$ pytest -v test_server.py::TestClass test_server.py::test_send_http
platform linux -- Python 3.x.y, pytest-6.x.y, py-1.x.y, pluggy-0.x.y -- $PYTHON_PREFIX/bin/python
cachedir: $PYTHON_PREFIX/.pytest_cache
rootdir: $REGENDOC_TMPDIR
collecting ... collected 2 items

test_server.py::TestClass::test_method PASSED                        [ 50%]
test_server.py::test_send_http PASSED                                [100%]

::: {#node-id}
::: {.note}
::: {.title}
Note
:::

Node IDs are of the form module.py::class::method or
module.py::function. Node IDs control which tests are collected, so
module.py::class will select all test methods on the class. Nodes are
also created for each parameter of a parametrized fixture or test, so
selecting a parametrized test must include the parameter value, e.g.
module.py::function[param].

Node IDs for failing tests are displayed in the test summary info when
running pytest with the -rf option. You can also construct Node IDs
from the output of pytest --collectonly.
:::
:::

Using -k expr to select tests based on their name

::: {.versionadded}
2.0/2.3.4
:::

You can use the -k command line option to specify an expression which
implements a substring match on the test names instead of the exact
match on markers that -m provides. This makes it easy to select tests
based on their names:

::: {.versionchanged}
5.4
:::

The expression matching is now case-insensitive.

$ pytest -v -k http  # running with the above defined example module
platform linux -- Python 3.x.y, pytest-6.x.y, py-1.x.y, pluggy-0.x.y -- $PYTHON_PREFIX/bin/python
cachedir: $PYTHON_PREFIX/.pytest_cache
rootdir: $REGENDOC_TMPDIR
collecting ... collected 4 items / 3 deselected / 1 selected

test_server.py::test_send_http PASSED                                [100%]

And you can also run all tests except the ones that match the keyword:

$ pytest -k "not send_http" -v
platform linux -- Python 3.x.y, pytest-6.x.y, py-1.x.y, pluggy-0.x.y -- $PYTHON_PREFIX/bin/python
cachedir: $PYTHON_PREFIX/.pytest_cache
rootdir: $REGENDOC_TMPDIR
collecting ... collected 4 items / 1 deselected / 3 selected

test_server.py::test_something_quick PASSED                          [ 33%]
test_server.py::test_another PASSED                                  [ 66%]
test_server.py::TestClass::test_method PASSED                        [100%]

Or to select “http” and “quick” tests:

$ pytest -k "http or quick" -v
platform linux -- Python 3.x.y, pytest-6.x.y, py-1.x.y, pluggy-0.x.y -- $PYTHON_PREFIX/bin/python
cachedir: $PYTHON_PREFIX/.pytest_cache
rootdir: $REGENDOC_TMPDIR
collecting ... collected 4 items / 2 deselected / 2 selected

test_server.py::test_send_http PASSED                                [ 50%]
test_server.py::test_something_quick PASSED                          [100%]

You can use and, or, not and parentheses.

In addition to the test’s name, -k also matches the names of the
test’s parents (usually, the name of the file and class it’s in),
attributes set on the test function, markers applied to it or its
parents and any
extra keywords <_pytest.nodes.Node.extra_keyword_matches>{.interpreted-text
role=“attr”} explicitly added to it or its parents.

Registering markers

Registering markers for your test suite is simple:

# content of pytest.ini
[pytest]
markers =
    webtest: mark a test as a webtest.
    slow: mark test as slow.

Multiple custom markers can be registered, by defining each one in its
own line, as shown in above example.

You can ask which markers exist for your test suite - the list includes
our just defined webtest and slow markers:

$ pytest --markers
@pytest.mark.webtest: mark a test as a webtest.

@pytest.mark.slow: mark test as slow.

@pytest.mark.filterwarnings(warning): add a warning filter to the given test. see https://docs.pytest.org/en/stable/warnings.html#pytest-mark-filterwarnings

@pytest.mark.skip(reason=None): skip the given test function with an optional reason. Example: skip(reason="no way of currently testing this") skips the test.


@pytest.mark.xfail(condition, ..., *, reason=..., run=True, raises=None, strict=xfail_strict): mark the test function as an expected failure if any of the conditions evaluate to True. Optionally specify a reason for better reporting and run=False if you don't even want to execute the test function. If only specific exception(s) are expected, you can list them in raises, and if the test fails in other ways, it will be reported as a true failure. See https://docs.pytest.org/en/stable/reference.html#pytest-mark-xfail

@pytest.mark.parametrize(argnames, argvalues): call a test function multiple times passing in different arguments in turn. argvalues generally needs to be a list of values if argnames specifies only one name or a list of tuples of values if argnames specifies multiple names. Example: @parametrize('arg1', [1,2]) would lead to two calls of the decorated test function, one with arg1=1 and another with arg1=2.see https://docs.pytest.org/en/stable/parametrize.html for more info and examples.

@pytest.mark.usefixtures(fixturename1, fixturename2, ...): mark tests as needing all of the specified fixtures. see https://docs.pytest.org/en/stable/fixture.html#usefixtures

@pytest.mark.tryfirst: mark a hook implementation function such that the plugin machinery will try to call it first/as early as possible.

@pytest.mark.trylast: mark a hook implementation function such that the plugin machinery will try to call it last/as late as possible.

For an example on how to add and work with markers from a plugin, see
adding a custom marker from a plugin{.interpreted-text role=“ref”}.

::: {.note}
::: {.title}
Note
:::

It is recommended to explicitly register markers so that:

  • There is one place in your test suite defining your markers
  • Asking for existing markers via pytest --markers gives good output
  • Typos in function markers are treated as an error if you use the
    --strict-markers option.
    :::

Marking whole classes or modules {#scoped-marking}

You may use pytest.mark decorators with classes to apply markers to
all of its test methods:

# content of test_mark_classlevel.py
import pytest


@pytest.mark.webtest
class TestClass:
    def test_startup(self):
        pass

    def test_startup_and_more(self):
        pass

This is equivalent to directly applying the decorator to the two test
functions.

To apply marks at the module level, use the
pytestmark{.interpreted-text role=“globalvar”} global variable:

import pytest
pytestmark = pytest.mark.webtest

or multiple markers:

pytestmark = [pytest.mark.webtest, pytest.mark.slowtest]

Due to legacy reasons, before class decorators were introduced, it is
possible to set the pytestmark{.interpreted-text role=“globalvar”}
attribute on a test class like this:

import pytest


class TestClass:
    pytestmark = pytest.mark.webtest

Marking individual tests when using parametrize {#marking individual tests when using parametrize}

When using parametrize, applying a mark will make it apply to each
individual test. However it is also possible to apply a marker to an
individual test instance:

import pytest


@pytest.mark.foo
@pytest.mark.parametrize(
    ("n", "expected"), [(1, 2), pytest.param(1, 3, marks=pytest.mark.bar), (2, 3)]
)
def test_increment(n, expected):

In this example the mark “foo” will apply to each of the three tests,
whereas the “bar” mark is only applied to the second test. Skip and
xfail marks can also be applied in this way, see
skip/xfail with parametrize{.interpreted-text role=“ref”}.

Custom marker and command line option to control test runs {#adding a custom marker from a plugin}

Plugins can provide custom markers and implement specific behaviour
based on it. This is a self-contained example which adds a command line
option and a parametrized test function marker to run tests specifies
via named environments:

# content of conftest.py

import pytest


def pytest_addoption(parser):
    parser.addoption(
        "-E",
        action="store",
        metavar="NAME",
        help="only run tests matching the environment NAME.",
    )


def pytest_configure(config):
    # register an additional marker
    config.addinivalue_line(
        "markers", "env(name): mark test to run only on named environment"
    )


def pytest_runtest_setup(item):
    envnames = [mark.args[0] for mark in item.iter_markers(name="env")]
    if envnames:
        if item.config.getoption("-E") not in envnames:
            pytest.skip("test requires env in {!r}".format(envnames))

A test file using this local plugin:

# content of test_someenv.py

import pytest


@pytest.mark.env("stage1")
def test_basic_db_operation():
    pass

and an example invocations specifying a different environment than what
the test needs:

$ pytest -E stage2
platform linux -- Python 3.x.y, pytest-6.x.y, py-1.x.y, pluggy-0.x.y
cachedir: $PYTHON_PREFIX/.pytest_cache
rootdir: $REGENDOC_TMPDIR
collected 1 item

test_someenv.py s                                                    [100%]

and here is one that specifies exactly the environment needed:

$ pytest -E stage1
platform linux -- Python 3.x.y, pytest-6.x.y, py-1.x.y, pluggy-0.x.y
cachedir: $PYTHON_PREFIX/.pytest_cache
rootdir: $REGENDOC_TMPDIR
collected 1 item

test_someenv.py .                                                    [100%]

The --markers option always gives you a list of available markers:

$ pytest --markers
@pytest.mark.env(name): mark test to run only on named environment

@pytest.mark.filterwarnings(warning): add a warning filter to the given test. see https://docs.pytest.org/en/stable/warnings.html#pytest-mark-filterwarnings

@pytest.mark.skip(reason=None): skip the given test function with an optional reason. Example: skip(reason="no way of currently testing this") skips the test.


@pytest.mark.xfail(condition, ..., *, reason=..., run=True, raises=None, strict=xfail_strict): mark the test function as an expected failure if any of the conditions evaluate to True. Optionally specify a reason for better reporting and run=False if you don't even want to execute the test function. If only specific exception(s) are expected, you can list them in raises, and if the test fails in other ways, it will be reported as a true failure. See https://docs.pytest.org/en/stable/reference.html#pytest-mark-xfail

@pytest.mark.parametrize(argnames, argvalues): call a test function multiple times passing in different arguments in turn. argvalues generally needs to be a list of values if argnames specifies only one name or a list of tuples of values if argnames specifies multiple names. Example: @parametrize('arg1', [1,2]) would lead to two calls of the decorated test function, one with arg1=1 and another with arg1=2.see https://docs.pytest.org/en/stable/parametrize.html for more info and examples.

@pytest.mark.usefixtures(fixturename1, fixturename2, ...): mark tests as needing all of the specified fixtures. see https://docs.pytest.org/en/stable/fixture.html#usefixtures

@pytest.mark.tryfirst: mark a hook implementation function such that the plugin machinery will try to call it first/as early as possible.

@pytest.mark.trylast: mark a hook implementation function such that the plugin machinery will try to call it last/as late as possible.

Passing a callable to custom markers {#passing callables to custom markers}

Below is the config file that will be used in the next examples:

# content of conftest.py
import sys


def pytest_runtest_setup(item):
    for marker in item.iter_markers(name="my_marker"):
        print(marker)
        sys.stdout.flush()

A custom marker can have its argument set, i.e. args and kwargs
properties, defined by either invoking it as a callable or using
pytest.mark.MARKER_NAME.with_args. These two methods achieve the same
effect most of the time.

However, if there is a callable as the single positional argument with
no keyword arguments, using the pytest.mark.MARKER_NAME(c) will not
pass c as a positional argument but decorate c with the custom
marker (see MarkDecorator <mark>{.interpreted-text role=“ref”}).
Fortunately, pytest.mark.MARKER_NAME.with_args comes to the rescue:

# content of test_custom_marker.py
import pytest


def hello_world(*args, **kwargs):
    return "Hello World"


@pytest.mark.my_marker.with_args(hello_world)
def test_with_args():
    pass

The output is as follows:

$ pytest -q -s
Mark(name='my_marker', args=(<function hello_world at 0xdeadbeef>,), kwargs={})
.
1 passed in 0.12s

We can see that the custom marker has its argument set extended with the
function hello_world. This is the key difference between creating a
custom marker as a callable, which invokes __call__ behind the scenes,
and using with_args.

Reading markers which were set from multiple places

If you are heavily using markers in your test suite you may encounter
the case where a marker is applied several times to a test function.
From plugin code you can read over all such settings. Example:

# content of test_mark_three_times.py
import pytest

pytestmark = pytest.mark.glob("module", x=1)


@pytest.mark.glob("class", x=2)
class TestClass:
    @pytest.mark.glob("function", x=3)
    def test_something(self):
        pass

Here we have the marker “glob” applied three times to the same test
function. From a conftest file we can read it like this:

# content of conftest.py
import sys


def pytest_runtest_setup(item):
    for mark in item.iter_markers(name="glob"):
        print("glob args={} kwargs={}".format(mark.args, mark.kwargs))
        sys.stdout.flush()

Let’s run this without capturing output and see what we get:

$ pytest -q -s
glob args=('function',) kwargs={'x': 3}
glob args=('class',) kwargs={'x': 2}
glob args=('module',) kwargs={'x': 1}
.
1 passed in 0.12s

Marking platform specific tests with pytest

Consider you have a test suite which marks tests for particular
platforms, namely pytest.mark.darwin, pytest.mark.win32 etc. and you
also have tests that run on all platforms and have no specific marker.
If you now want to have a way to only run the tests for your particular
platform, you could use the following plugin:

# content of conftest.py
#
import sys
import pytest

ALL = set("darwin linux win32".split())


def pytest_runtest_setup(item):
    supported_platforms = ALL.intersection(mark.name for mark in item.iter_markers())
    plat = sys.platform
    if supported_platforms and plat not in supported_platforms:
        pytest.skip("cannot run on platform {}".format(plat))

then tests will be skipped if they were specified for a different
platform. Let’s do a little test file to show how this looks like:

# content of test_plat.py

import pytest


@pytest.mark.darwin
def test_if_apple_is_evil():
    pass


@pytest.mark.linux
def test_if_linux_works():
    pass


@pytest.mark.win32
def test_if_win32_crashes():
    pass


def test_runs_everywhere():
    pass

then you will see two tests skipped and two executed tests as expected:

$ pytest -rs # this option reports skip reasons
platform linux -- Python 3.x.y, pytest-6.x.y, py-1.x.y, pluggy-0.x.y
cachedir: $PYTHON_PREFIX/.pytest_cache
rootdir: $REGENDOC_TMPDIR
collected 4 items

test_plat.py s.s.                                                    [100%]

SKIPPED [2] conftest.py:12: cannot run on platform linux

Note that if you specify a platform via the marker-command line option
like this:

$ pytest -m linux
platform linux -- Python 3.x.y, pytest-6.x.y, py-1.x.y, pluggy-0.x.y
cachedir: $PYTHON_PREFIX/.pytest_cache
rootdir: $REGENDOC_TMPDIR
collected 4 items / 3 deselected / 1 selected

test_plat.py .                                                       [100%]

then the unmarked-tests will not be run. It is thus a way to restrict
the run to the specific tests.

Automatically adding markers based on test names

If you have a test suite where test function names indicate a certain
type of test, you can implement a hook that automatically defines
markers so that you can use the -m option with it. Let’s look at this
test module:

# content of test_module.py


def test_interface_simple():
    assert 0


def test_interface_complex():
    assert 0


def test_event_simple():
    assert 0


def test_something_else():
    assert 0

We want to dynamically define two markers and can do it in a
conftest.py plugin:

# content of conftest.py

import pytest


def pytest_collection_modifyitems(items):
    for item in items:
        if "interface" in item.nodeid:
            item.add_marker(pytest.mark.interface)
        elif "event" in item.nodeid:
            item.add_marker(pytest.mark.event)

We can now use the -m option to select one set:

$ pytest -m interface --tb=short
platform linux -- Python 3.x.y, pytest-6.x.y, py-1.x.y, pluggy-0.x.y
cachedir: $PYTHON_PREFIX/.pytest_cache
rootdir: $REGENDOC_TMPDIR
collected 4 items / 2 deselected / 2 selected

test_module.py FF                                                    [100%]

__________________________ test_interface_simple ___________________________
test_module.py:4: in test_interface_simple
    assert 0
E   assert 0
__________________________ test_interface_complex __________________________
test_module.py:8: in test_interface_complex
    assert 0
E   assert 0
FAILED test_module.py::test_interface_simple - assert 0
FAILED test_module.py::test_interface_complex - assert 0

or to select both “event” and “interface” tests:

$ pytest -m "interface or event" --tb=short
platform linux -- Python 3.x.y, pytest-6.x.y, py-1.x.y, pluggy-0.x.y
cachedir: $PYTHON_PREFIX/.pytest_cache
rootdir: $REGENDOC_TMPDIR
collected 4 items / 1 deselected / 3 selected

test_module.py FFF                                                   [100%]

__________________________ test_interface_simple ___________________________
test_module.py:4: in test_interface_simple
    assert 0
E   assert 0
__________________________ test_interface_complex __________________________
test_module.py:8: in test_interface_complex
    assert 0
E   assert 0
____________________________ test_event_simple _____________________________
test_module.py:12: in test_event_simple
    assert 0
E   assert 0
FAILED test_module.py::test_interface_simple - assert 0
FAILED test_module.py::test_interface_complex - assert 0
FAILED test_module.py::test_event_simple - assert 0
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