Usage and Invocations

Calling pytest through python -m pytest

New in version 2.0.

If you use Python-2.5 or later 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 test_mod.py   # run tests in module
py.test somepath      # run all tests below somepath
py.test -k stringexpr # only run tests with names that match the
                      # the "string expression", e.g. "MyClass and not method"
                      # will select TestMyClass.test_something
                      # but not TestMyClass.test_method_simple
py.test test_mod.py::test_func  # only run tests that match the "node ID",
                                # e.g "test_mod.py::test_func" will select
                                # only test_func in test_mod.py

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. 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

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 occuring 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 Hudson or other Continuous 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.

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 http://bpaste.net 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:

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_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 myinvoke.py
*** test run reporting finishing