Basic patterns and examples¶

How to change command line options defaults¶

It can be tedious to type the same series of command line options every time you use pytest. For example, if you always want to see detailed info on skipped and xfailed tests, as well as have terser “dot” progress output, you can write it into a configuration file:

# content of pytest.ini
[pytest]
addopts = -ra -q

Alternatively, you can set a PYTEST_ADDOPTS environment variable to add command line options while the environment is in use:

export PYTEST_ADDOPTS="-v"

Here’s how the command-line is built in the presence of addopts or the environment variable:

<pytest.ini:addopts> $PYTEST_ADDOPTS <extra command-line arguments>

So if the user executes in the command-line:

pytest -m slow

The actual command line executed is:

pytest -ra -q -v -m slow

Note that as usual for other command-line applications, in case of conflicting options the last one wins, so the example above will show verbose output because -v overwrites -q.

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

Suppose we want to write a test that depends on a command line option. Here is a basic pattern 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 fixture function:

# content of conftest.py
import pytest


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


@pytest.fixture
def cmdopt(request):
    return request.config.getoption("--cmdopt")

Let’s run this without supplying our new option:

$ pytest -q test_sample.py
F                                                                    [100%]
================================= 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 call ---------------------------
first
========================= short test summary info ==========================
FAILED test_sample.py::test_answer - assert 0
1 failed in 0.12s

And now with supplying a command line option:

$ pytest -q --cmdopt=type2
F                                                                    [100%]
================================= 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 call ---------------------------
second
========================= short test summary info ==========================
FAILED test_sample.py::test_answer - assert 0
1 failed in 0.12s

You can see that the command line option arrived in our test.

We could add simple validation for the input by listing the choices:

# content of conftest.py
import pytest


def pytest_addoption(parser):
    parser.addoption(
        "--cmdopt",
        action="store",
        default="type1",
        help="my option: type1 or type2",
        choices=("type1", "type2"),
    )

Now we’ll get feedback on a bad argument:

$ pytest -q --cmdopt=type3
ERROR: usage: pytest [options] [file_or_dir] [file_or_dir] [...]
pytest: error: argument --cmdopt: invalid choice: 'type3' (choose from 'type1', 'type2')

If you need to provide more detailed error messages, you can use the type parameter and raise pytest.UsageError:

# content of conftest.py
import pytest


def type_checker(value):
    msg = "cmdopt must specify a numeric type as typeNNN"
    if not value.startswith("type"):
        raise pytest.UsageError(msg)
    try:
        int(value[4:])
    except ValueError:
        raise pytest.UsageError(msg)

    return value


def pytest_addoption(parser):
    parser.addoption(
        "--cmdopt",
        action="store",
        default="type1",
        help="my option: type1 or type2",
        type=type_checker,
    )

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.

Dynamically adding command line options¶

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

# setuptools plugin
import sys


def pytest_load_initial_conftests(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 xdist plugin 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:

$ pytest
=========================== test session starts ============================
platform linux -- Python 3.x.y, pytest-7.x.y, pluggy-1.x.y
rootdir: /home/sweet/project
collected 0 items

========================== no tests ran in 0.12s ===========================

Control skipping of tests according to command line option¶

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

# content of conftest.py

import pytest


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


def pytest_configure(config):
    config.addinivalue_line("markers", "slow: mark test as slow to run")


def pytest_collection_modifyitems(config, items):
    if config.getoption("--runslow"):
        # --runslow given in cli: do not skip slow tests
        return
    skip_slow = pytest.mark.skip(reason="need --runslow option to run")
    for item in items:
        if "slow" in item.keywords:
            item.add_marker(skip_slow)

We can now write a test module like this:

# content of test_module.py
import pytest


def test_func_fast():
    pass


@pytest.mark.slow
def test_func_slow():
    pass

and when running it will see a skipped “slow” test:

$ pytest -rs    # "-rs" means report details on the little 's'
=========================== test session starts ============================
platform linux -- Python 3.x.y, pytest-7.x.y, pluggy-1.x.y
rootdir: /home/sweet/project
collected 2 items

test_module.py .s                                                    [100%]

========================= short test summary info ==========================
SKIPPED [1] test_module.py:8: need --runslow option to run
======================= 1 passed, 1 skipped in 0.12s =======================

Or run it including the slow marked test:

$ pytest --runslow
=========================== test session starts ============================
platform linux -- Python 3.x.y, pytest-7.x.y, pluggy-1.x.y
rootdir: /home/sweet/project
collected 2 items

test_module.py ..                                                    [100%]

============================ 2 passed in 0.12s =============================

Writing well integrated assertion helpers¶

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(f"not configured: {x}")


def test_something():
    checkconfig(42)

The __tracebackhide__ setting influences pytest showing of tracebacks: the checkconfig function will not be shown unless the --full-trace command line option is specified. Let’s run our little function:

$ pytest -q test_checkconfig.py
F                                                                    [100%]
================================= FAILURES =================================
______________________________ test_something ______________________________

    def test_something():
>       checkconfig(42)
E       Failed: not configured: 42

test_checkconfig.py:11: Failed
========================= short test summary info ==========================
FAILED test_checkconfig.py::test_something - Failed: not configured: 42
1 failed in 0.12s

If you only want to hide certain exceptions, you can set __tracebackhide__ to a callable which gets the ExceptionInfo object. You can for example use this to make sure unexpected exception types aren’t hidden:

import operator

import pytest

class ConfigException(Exception):
    pass

def checkconfig(x):
    __tracebackhide__ = operator.methodcaller("errisinstance", ConfigException)
    if not hasattr(x, "config"):
        raise ConfigException(f"not configured: {x}")

def test_something():
    checkconfig(42)

This will avoid hiding the exception traceback on unrelated exceptions (i.e. bugs in assertion helpers).

Detect if running from within a pytest run¶

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 your_module.py

_called_from_test = False

# content of conftest.py


def pytest_configure(config):
    your_module._called_from_test = True

and then check for the your_module._called_from_test flag:

if your_module._called_from_test:
    # called from within a test run
    ...
else:
    # called "normally"
    ...

accordingly in your application.

Adding info to test report header¶

It’s easy to present extra information in a pytest 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:

$ pytest
=========================== test session starts ============================
platform linux -- Python 3.x.y, pytest-7.x.y, pluggy-1.x.y
project deps: mylib-1.1
rootdir: /home/sweet/project
collected 0 items

========================== no tests ran in 0.12s ===========================

It is also possible to return a list of strings which will be considered as several lines of information. You may consider config.getoption('verbose') in order to display more information if applicable:

# content of conftest.py


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

which will add info only when run with “–v”:

$ pytest -v
=========================== test session starts ============================
platform linux -- Python 3.x.y, pytest-7.x.y, pluggy-1.x.y -- $PYTHON_PREFIX/bin/python
cachedir: .pytest_cache
info1: did you know that ...
did you?
rootdir: /home/sweet/project
collecting ... collected 0 items

========================== no tests ran in 0.12s ===========================

and nothing when run plainly:

$ pytest
=========================== test session starts ============================
platform linux -- Python 3.x.y, pytest-7.x.y, pluggy-1.x.y
rootdir: /home/sweet/project
collected 0 items

========================== no tests ran in 0.12s ===========================

Profiling test duration¶

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

# content of test_some_are_slow.py
import time

def test_funcfast():
    time.sleep(0.1)

def test_funcslow1():
    time.sleep(0.2)

def test_funcslow2():
    time.sleep(0.3)

Now we can profile which test functions execute the slowest:

$ pytest --durations=3
=========================== test session starts ============================
platform linux -- Python 3.x.y, pytest-7.x.y, pluggy-1.x.y
rootdir: /home/sweet/project
collected 3 items

test_some_are_slow.py ...                                            [100%]

=========================== slowest 3 durations ============================
0.30s call     test_some_are_slow.py::test_funcslow2
0.20s call     test_some_are_slow.py::test_funcslow1
0.10s call     test_some_are_slow.py::test_funcfast
============================ 3 passed in 0.12s =============================

Incremental testing - test steps¶

Sometimes you may have a testing situation which consists of a series of test steps. If one step fails it makes no sense to execute further steps as they are all expected to fail anyway and their tracebacks add no insight. Here is a simple conftest.py file which introduces an incremental marker which is to be used on classes:

# content of conftest.py

from typing import Dict, Tuple

import pytest

# store history of failures per test class name and per index in parametrize (if parametrize used)
_test_failed_incremental: Dict[str, Dict[Tuple[int, ...], str]] = {}


def pytest_runtest_makereport(item, call):
    if "incremental" in item.keywords:
        # incremental marker is used
        if call.excinfo is not None:
            # the test has failed
            # retrieve the class name of the test
            cls_name = str(item.cls)
            # retrieve the index of the test (if parametrize is used in combination with incremental)
            parametrize_index = (
                tuple(item.callspec.indices.values())
                if hasattr(item, "callspec")
                else ()
            )
            # retrieve the name of the test function
            test_name = item.originalname or item.name
            # store in _test_failed_incremental the original name of the failed test
            _test_failed_incremental.setdefault(cls_name, {}).setdefault(
                parametrize_index, test_name
            )


def pytest_runtest_setup(item):
    if "incremental" in item.keywords:
        # retrieve the class name of the test
        cls_name = str(item.cls)
        # check if a previous test has failed for this class
        if cls_name in _test_failed_incremental:
            # retrieve the index of the test (if parametrize is used in combination with incremental)
            parametrize_index = (
                tuple(item.callspec.indices.values())
                if hasattr(item, "callspec")
                else ()
            )
            # retrieve the name of the first test function to fail for this class name and index
            test_name = _test_failed_incremental[cls_name].get(parametrize_index, None)
            # if name found, test has failed for the combination of class name & test name
            if test_name is not None:
                pytest.xfail(f"previous test failed ({test_name})")

These two hook implementations work together to abort incremental-marked tests in a class. Here is a test module example:

# content of test_step.py

import pytest


@pytest.mark.incremental
class TestUserHandling:
    def test_login(self):
        pass

    def test_modification(self):
        assert 0

    def test_deletion(self):
        pass


def test_normal():
    pass

If we run this:

$ pytest -rx
=========================== test session starts ============================
platform linux -- Python 3.x.y, pytest-7.x.y, pluggy-1.x.y
rootdir: /home/sweet/project
collected 4 items

test_step.py .Fx.                                                    [100%]

================================= FAILURES =================================
____________________ TestUserHandling.test_modification ____________________

self = <test_step.TestUserHandling object at 0xdeadbeef0001>

    def test_modification(self):
>       assert 0
E       assert 0

test_step.py:11: AssertionError
========================= short test summary info ==========================
XFAIL test_step.py::TestUserHandling::test_deletion
  reason: previous test failed (test_modification)
================== 1 failed, 2 passed, 1 xfailed in 0.12s ==================

We’ll see that test_deletion was not executed because test_modification failed. It is reported as an “expected failure”.

Package/Directory-level fixtures (setups)¶

If you have nested test directories, you can have per-directory fixture scopes by placing fixture functions in a conftest.py file in that directory. You can use all types of fixtures including autouse fixtures which are the equivalent of xUnit’s setup/teardown concept. It’s however recommended to have explicit fixture references in your tests or test classes rather than relying on implicitly executing setup/teardown functions, especially if they are far away from the actual tests.

Here is an example for making a db fixture available in a directory:

# content of a/conftest.py
import pytest


class DB:
    pass


@pytest.fixture(scope="session")
def db():
    return DB()

and then a test module in that directory:

# content of a/test_db.py
def test_a1(db):
    assert 0, db  # to show value

another test module:

# content of a/test_db2.py
def test_a2(db):
    assert 0, db  # to show value

and then a module in a sister directory which will not see the db fixture:

# content of b/test_error.py
def test_root(db):  # no db here, will error out
    pass

We can run this:

$ pytest
=========================== test session starts ============================
platform linux -- Python 3.x.y, pytest-7.x.y, pluggy-1.x.y
rootdir: /home/sweet/project
collected 7 items

test_step.py .Fx.                                                    [ 57%]
a/test_db.py F                                                       [ 71%]
a/test_db2.py F                                                      [ 85%]
b/test_error.py E                                                    [100%]

================================== ERRORS ==================================
_______________________ ERROR at setup of test_root ________________________
file /home/sweet/project/b/test_error.py, line 1
  def test_root(db):  # no db here, will error out
E       fixture 'db' not found
>       available fixtures: cache, capfd, capfdbinary, caplog, capsys, capsysbinary, doctest_namespace, monkeypatch, pytestconfig, record_property, record_testsuite_property, record_xml_attribute, recwarn, tmp_path, tmp_path_factory, tmpdir, tmpdir_factory
>       use 'pytest --fixtures [testpath]' for help on them.

/home/sweet/project/b/test_error.py:1
================================= FAILURES =================================
____________________ TestUserHandling.test_modification ____________________

self = <test_step.TestUserHandling object at 0xdeadbeef0002>

    def test_modification(self):
>       assert 0
E       assert 0

test_step.py:11: AssertionError
_________________________________ test_a1 __________________________________

db = <conftest.DB object at 0xdeadbeef0003>

    def test_a1(db):
>       assert 0, db  # to show value
E       AssertionError: <conftest.DB object at 0xdeadbeef0003>
E       assert 0

a/test_db.py:2: AssertionError
_________________________________ test_a2 __________________________________

db = <conftest.DB object at 0xdeadbeef0003>

    def test_a2(db):
>       assert 0, db  # to show value
E       AssertionError: <conftest.DB object at 0xdeadbeef0003>
E       assert 0

a/test_db2.py:2: AssertionError
========================= short test summary info ==========================
FAILED test_step.py::TestUserHandling::test_modification - assert 0
FAILED a/test_db.py::test_a1 - AssertionError: <conftest.DB object at 0x7...
FAILED a/test_db2.py::test_a2 - AssertionError: <conftest.DB object at 0x...
ERROR b/test_error.py::test_root
============= 3 failed, 2 passed, 1 xfailed, 1 error in 0.12s ==============

The two test modules in the a directory see the same db fixture instance while the one test in the sister-directory b doesn’t see it. We could of course also define a db fixture in that sister directory’s conftest.py file. Note that each fixture is only instantiated if there is a test actually needing it (unless you use “autouse” fixture which are always executed ahead of the first test executing).

Post-process test reports / failures¶

If you want to postprocess test reports and need access to the executing environment you can implement a hook that gets called when the test “report” object is about to be created. Here we write out all failing test calls and also access a fixture (if it was used by the test) in case you want to query/look at it during your post processing. In our case we just write some information out to a failures file:

# content of conftest.py

import os.path

import pytest


@pytest.hookimpl(tryfirst=True, hookwrapper=True)
def pytest_runtest_makereport(item, call):
    # execute all other hooks to obtain the report object
    outcome = yield
    rep = outcome.get_result()

    # we only look at actual failing test calls, not setup/teardown
    if rep.when == "call" and rep.failed:
        mode = "a" if os.path.exists("failures") else "w"
        with open("failures", mode) as f:
            # let's also access a fixture for the fun of it
            if "tmp_path" in item.fixturenames:
                extra = " ({})".format(item.funcargs["tmp_path"])
            else:
                extra = ""

            f.write(rep.nodeid + extra + "\n")

if you then have failing tests:

# content of test_module.py
def test_fail1(tmp_path):
    assert 0


def test_fail2():
    assert 0

and run them:

$ pytest test_module.py
=========================== test session starts ============================
platform linux -- Python 3.x.y, pytest-7.x.y, pluggy-1.x.y
rootdir: /home/sweet/project
collected 2 items

test_module.py FF                                                    [100%]

================================= FAILURES =================================
________________________________ test_fail1 ________________________________

tmp_path = PosixPath('PYTEST_TMPDIR/test_fail10')

    def test_fail1(tmp_path):
>       assert 0
E       assert 0

test_module.py:2: AssertionError
________________________________ test_fail2 ________________________________

    def test_fail2():
>       assert 0
E       assert 0

test_module.py:6: AssertionError
========================= short test summary info ==========================
FAILED test_module.py::test_fail1 - assert 0
FAILED test_module.py::test_fail2 - assert 0
============================ 2 failed in 0.12s =============================

you will have a “failures” file which contains the failing test ids:

$ cat failures
test_module.py::test_fail1 (PYTEST_TMPDIR/test_fail10)
test_module.py::test_fail2

Making test result information available in fixtures¶

If you want to make test result reports available in fixture finalizers here is a little example implemented via a local plugin:

# content of conftest.py

import pytest


@pytest.hookimpl(tryfirst=True, hookwrapper=True)
def pytest_runtest_makereport(item, call):
    # execute all other hooks to obtain the report object
    outcome = yield
    rep = outcome.get_result()

    # set a report attribute for each phase of a call, which can
    # be "setup", "call", "teardown"

    setattr(item, "rep_" + rep.when, rep)


@pytest.fixture
def something(request):
    yield
    # request.node is an "item" because we use the default
    # "function" scope
    if request.node.rep_setup.failed:
        print("setting up a test failed!", request.node.nodeid)
    elif request.node.rep_setup.passed:
        if request.node.rep_call.failed:
            print("executing test failed", request.node.nodeid)

if you then have failing tests:

# content of test_module.py

import pytest

@pytest.fixture
def other():
    assert 0

def test_setup_fails(something, other):
    pass

def test_call_fails(something):
    assert 0

def test_fail2():
    assert 0

and run it:

$ pytest -s test_module.py
=========================== test session starts ============================
platform linux -- Python 3.x.y, pytest-7.x.y, pluggy-1.x.y
rootdir: /home/sweet/project
collected 3 items

test_module.py Esetting up a test failed! test_module.py::test_setup_fails
Fexecuting test failed test_module.py::test_call_fails
F

================================== ERRORS ==================================
____________________ ERROR at setup of test_setup_fails ____________________

    @pytest.fixture
    def other():
>       assert 0
E       assert 0

test_module.py:7: AssertionError
================================= FAILURES =================================
_____________________________ test_call_fails ______________________________

something = None

    def test_call_fails(something):
>       assert 0
E       assert 0

test_module.py:15: AssertionError
________________________________ test_fail2 ________________________________

    def test_fail2():
>       assert 0
E       assert 0

test_module.py:19: AssertionError
========================= short test summary info ==========================
FAILED test_module.py::test_call_fails - assert 0
FAILED test_module.py::test_fail2 - assert 0
ERROR test_module.py::test_setup_fails - assert 0
======================== 2 failed, 1 error in 0.12s ========================

You’ll see that the fixture finalizers could use the precise reporting information.

`PYTEST_CURRENT_TEST` environment variable¶

Sometimes a test session might get stuck and there might be no easy way to figure out which test got stuck, for example if pytest was run in quiet mode (-q) or you don’t have access to the console output. This is particularly a problem if the problem happens only sporadically, the famous “flaky” kind of tests.

pytest sets the PYTEST_CURRENT_TEST environment variable when running tests, which can be inspected by process monitoring utilities or libraries like psutil to discover which test got stuck if necessary:

import psutil

for pid in psutil.pids():
    environ = psutil.Process(pid).environ()
    if "PYTEST_CURRENT_TEST" in environ:
        print(f'pytest process {pid} running: {environ["PYTEST_CURRENT_TEST"]}')

During the test session pytest will set PYTEST_CURRENT_TEST to the current test nodeid and the current stage, which can be setup, call, or teardown.

For example, when running a single test function named test_foo from foo_module.py, PYTEST_CURRENT_TEST will be set to:

foo_module.py::test_foo (setup)
foo_module.py::test_foo (call)
foo_module.py::test_foo (teardown)

In that order.

备注

The contents of PYTEST_CURRENT_TEST is meant to be human readable and the actual format can be changed between releases (even bug fixes) so it shouldn’t be relied on for scripting or automation.

Freezing pytest¶

If you freeze your application using a tool like PyInstaller in order to distribute it to your end-users, it is a good idea to also package your test runner and run your tests using the frozen application. This way packaging errors such as dependencies not being included into the executable can be detected early while also allowing you to send test files to users so they can run them in their machines, which can be useful to obtain more information about a hard to reproduce bug.

Fortunately recent PyInstaller releases already have a custom hook for pytest, but if you are using another tool to freeze executables such as cx_freeze or py2exe, you can use pytest.freeze_includes() to obtain the full list of internal pytest modules. How to configure the tools to find the internal modules varies from tool to tool, however.

Instead of freezing the pytest runner as a separate executable, you can make your frozen program work as the pytest runner by some clever argument handling during program startup. This allows you to have a single executable, which is usually more convenient. Please note that the mechanism for plugin discovery used by pytest (setuptools entry points) doesn’t work with frozen executables so pytest can’t find any third party plugins automatically. To include third party plugins like pytest-timeout they must be imported explicitly and passed on to pytest.main.

# contents of app_main.py
import sys

import pytest_timeout  # Third party plugin

if len(sys.argv) > 1 and sys.argv[1] == "--pytest":
    import pytest

    sys.exit(pytest.main(sys.argv[2:], plugins=[pytest_timeout]))
else:
    # normal application execution: at this point argv can be parsed
    # by your argument-parsing library of choice as usual
    ...

This allows you to execute tests using the frozen application with standard pytest command-line options:

./app_main --pytest --verbose --tb=long --junitxml=results.xml test-suite/

Basic patterns and examples¶

How to change command line options defaults¶

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

Dynamically adding command line options¶

Control skipping of tests according to command line option¶

Writing well integrated assertion helpers¶

Detect if running from within a pytest run¶

Adding info to test report header¶

Profiling test duration¶

Incremental testing - test steps¶

Package/Directory-level fixtures (setups)¶

Post-process test reports / failures¶

Making test result information available in fixtures¶

`PYTEST_CURRENT_TEST` environment variable¶

Freezing pytest¶

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Basic patterns and examples¶

How to change command line options defaults¶

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

Dynamically adding command line options¶

Control skipping of tests according to command line option¶

Writing well integrated assertion helpers¶

Detect if running from within a pytest run¶

Adding info to test report header¶

Profiling test duration¶

Incremental testing - test steps¶

Package/Directory-level fixtures (setups)¶

Post-process test reports / failures¶

Making test result information available in fixtures¶

PYTEST_CURRENT_TEST environment variable¶

Freezing pytest¶

`PYTEST_CURRENT_TEST` environment variable¶