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 equivalent to invoking the command line script py.test [...] directly.

Getting help on version, option names, environment variables

py.test --version   # shows where pytest was imported from
py.test --fixtures  # show available builtin function arguments
py.test -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:

py.test -x            # stop after first failure
py.test --maxfail=2    # stop after two failures

Specifying tests / selecting tests

Several test run options:

py.test   # run tests in module
py.test somepath      # run all tests below somepath
py.test -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
py.test  # only run tests that match the "node ID",
                                # e.g "" will select
                                # only test_func in
py.test  # run a single method in
                                             # a single class

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

py.test --pyargs pkg # run all tests found below directory of pkg

Modifying Python traceback printing

Examples for modifying traceback printing:

py.test --showlocals # show local variables in tracebacks
py.test -l           # show local variables (shortcut)

py.test --tb=auto    # (default) 'long' tracebacks for the first and last
                     # entry, but 'short' style for the other entries
py.test --tb=long    # exhaustive, informative traceback formatting
py.test --tb=short   # shorter traceback format
py.test --tb=line    # only one line per failure
py.test --tb=native  # Python standard library formatting
py.test --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 KeyboardInterrrupt (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 catched 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:

py.test --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:

py.test -x --pdb   # drop to PDB on first failure, then end test session
py.test --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 py.test -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 py.test -s.

Profiling test execution duration

To get a list of the slowest 10 test durations:

py.test --durations=10

Creating JUnitXML format files

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

py.test --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.

Creating resultlog format files

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

py.test --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:

py.test --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:

py.test --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 py.test like this:

py.test -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 “py.test” 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'])

or pass in a string:

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