Usage and Invocations

Calling pytest through python -m pytest

New in version 2.0.

You can invoke testing through the Python interpreter from the command line:

python -m pytest [...]

This is almost equivalent to invoking the command line script pytest [...] directly, except that python will also add the current directory to sys.path.

Getting help on version, option names, environment variables

pytest --version   # shows where pytest was imported from
pytest --fixtures  # show available builtin function arguments
pytest -h | --help # show help on command line and config file options

Stopping after the first (or N) failures

To stop the testing process after the first (N) failures:

pytest -x            # stop after first failure
pytest --maxfail=2    # stop after two failures

Specifying tests / selecting tests

Several test run options:

pytest   # run tests in module
pytest somepath      # run all tests below somepath
pytest -k stringexpr # only run tests with names that match the
                      # "string expression", e.g. "MyClass and not method"
                      # will select TestMyClass.test_something
                      # but not TestMyClass.test_method_simple
pytest  # only run tests that match the "node ID",
                                # e.g. "" will select
                                # only test_func in
pytest  # run a single method in
                                             # a single class

Import ‘pkg’ and use its filesystem location to find and run tests:

pytest --pyargs pkg # run all tests found below directory of pkg

Modifying Python traceback printing

Examples for modifying traceback printing:

pytest --showlocals # show local variables in tracebacks
pytest -l           # show local variables (shortcut)

pytest --tb=auto    # (default) 'long' tracebacks for the first and last
                     # entry, but 'short' style for the other entries
pytest --tb=long    # exhaustive, informative traceback formatting
pytest --tb=short   # shorter traceback format
pytest --tb=line    # only one line per failure
pytest --tb=native  # Python standard library formatting
pytest --tb=no      # no traceback at all

The --full-trace causes very long traces to be printed on error (longer than --tb=long). It also ensures that a stack trace is printed on KeyboardInterrupt (Ctrl+C). This is very useful if the tests are taking too long and you interrupt them with Ctrl+C to find out where the tests are hanging. By default no output will be shown (because KeyboardInterrupt is caught by pytest). By using this option you make sure a trace is shown.

Dropping to PDB (Python Debugger) on failures

Python comes with a builtin Python debugger called PDB. pytest allows one to drop into the PDB prompt via a command line option:

pytest --pdb

This will invoke the Python debugger on every failure. Often you might only want to do this for the first failing test to understand a certain failure situation:

pytest -x --pdb   # drop to PDB on first failure, then end test session
pytest --pdb --maxfail=3  # drop to PDB for first three failures

Note that on any failure the exception information is stored on sys.last_value, sys.last_type and sys.last_traceback. In interactive use, this allows one to drop into postmortem debugging with any debug tool. One can also manually access the exception information, for example:

>>> import sys
>>> sys.last_traceback.tb_lineno
>>> sys.last_value
AssertionError('assert result == "ok"',)

Setting a breakpoint / aka set_trace()

If you want to set a breakpoint and enter the pdb.set_trace() you can use a helper:

import pytest
def test_function():
    pytest.set_trace()    # invoke PDB debugger and tracing

Prior to pytest version 2.0.0 you could only enter PDB tracing if you disabled capturing on the command line via pytest -s. In later versions, pytest automatically disables its output capture when you enter PDB tracing:

  • Output capture in other tests is not affected.
  • Any prior test output that has already been captured and will be processed as such.
  • Any later output produced within the same test will not be captured and will instead get sent directly to sys.stdout. Note that this holds true even for test output occurring after you exit the interactive PDB tracing session and continue with the regular test run.

Since pytest version 2.4.0 you can also use the native Python import pdb;pdb.set_trace() call to enter PDB tracing without having to use the pytest.set_trace() wrapper or explicitly disable pytest’s output capturing via pytest -s.

Profiling test execution duration

To get a list of the slowest 10 test durations:

pytest --durations=10

Creating JUnitXML format files

To create result files which can be read by Jenkins or other Continuous integration servers, use this invocation:

pytest --junitxml=path

to create an XML file at path.


New in version 2.8.

If you want to log additional information for a test, you can use the record_xml_property fixture:

def test_function(record_xml_property):
    record_xml_property("example_key", 1)
    assert 0

This will add an extra property example_key="1" to the generated testcase tag:

<testcase classname="test_function" file="" line="0" name="test_function" time="0.0009">
    <property name="example_key" value="1" />


This is an experimental feature, and its interface might be replaced by something more powerful and general in future versions. The functionality per-se will be kept, however.

Currently it does not work when used with the pytest-xdist plugin.

Also please note that using this feature will break any schema verification. This might be a problem when used with some CI servers.

LogXML: add_global_property

New in version 3.0.

If you want to add a properties node in the testsuite level, which may contains properties that are relevant to all testcases you can use LogXML.add_global_properties

import pytest

def log_global_env_facts(f):

    if pytest.config.pluginmanager.hasplugin('junitxml'):
        my_junit = getattr(pytest.config, '_xml', None)

    my_junit.add_global_property('ARCH', 'PPC')
    my_junit.add_global_property('STORAGE_TYPE', 'CEPH')

def start_and_prepare_env():

class TestMe:
    def test_foo(self):
        assert True

This will add a property node below the testsuite node to the generated xml:

<testsuite errors="0" failures="0" name="pytest" skips="0" tests="1" time="0.006">
    <property name="ARCH" value="PPC"/>
    <property name="STORAGE_TYPE" value="CEPH"/>
  <testcase classname="test_me.TestMe" file="" line="16" name="test_foo" time="0.000243663787842"/>


This is an experimental feature, and its interface might be replaced by something more powerful and general in future versions. The functionality per-se will be kept.

Creating resultlog format files

Deprecated since version 3.0: This option is rarely used and is scheduled for removal in 4.0.

To create plain-text machine-readable result files you can issue:

pytest --resultlog=path

and look at the content at the path location. Such files are used e.g. by the PyPy-test web page to show test results over several revisions.

Sending test report to online pastebin service

Creating a URL for each test failure:

pytest --pastebin=failed

This will submit test run information to a remote Paste service and provide a URL for each failure. You may select tests as usual or add for example -x if you only want to send one particular failure.

Creating a URL for a whole test session log:

pytest --pastebin=all

Currently only pasting to the service is implemented.

Disabling plugins

To disable loading specific plugins at invocation time, use the -p option together with the prefix no:.

Example: to disable loading the plugin doctest, which is responsible for executing doctest tests from text files, invoke pytest like this:

pytest -p no:doctest

Calling pytest from Python code

New in version 2.0.

You can invoke pytest from Python code directly:


this acts as if you would call “pytest” from the command line. It will not raise SystemExit but return the exitcode instead. You can pass in options and arguments:

pytest.main(['-x', 'mytestdir'])

You can specify additional plugins to pytest.main:

# content of
import pytest
class MyPlugin:
    def pytest_sessionfinish(self):
        print("*** test run reporting finishing")

pytest.main(["-qq"], plugins=[MyPlugin()])

Running it will show that MyPlugin was added and its hook was invoked:

$ python
*** test run reporting finishing