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Usage and Invocations

calling pytest through python -m pytest

New in version 2.0.

If you use Python-2.5 or above 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 vars

py.test --version   # shows where pytest was imported from
py.test --funcargs  # 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 test_mod.py   # run tests in module
py.test somepath      # run all tests below path
py.test -k string     # only run tests whose names contain a string

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

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

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=long    # the default informative traceback formatting
py.test --tb=native  # the Python standard library formatting
py.test --tb=short   # a shorter traceback format
py.test --tb=line    # only one line per failure

Dropping to PDB (Python Debugger) on failures

Python comes with a builtin Python debugger called PDB. py.test allows 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 the first three failures

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

In previous versions you could only enter PDB tracing if you disable capturing.

creating JUnitXML format files

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

py.test --junitxml=path

to create an XML file at path.

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.

send test report to pocoo 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 http://paste.pocoo.org service is implemented.

calling pytest from Python code

New in version 2.0.

You can invoke py.test from Python code directly:

pytest.main()

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 myinvoke.py
import pytest
class MyPlugin:
    def pytest_addoption(self, parser):
        raise pytest.UsageError("hi from our plugin")

pytest.main(plugins=[MyPlugin()])

Running it will exit quickly:

$ python myinvoke.py
ERROR: hi from our plugin