Good Integration Practises

Work with virtual environments

We recommend to use virtualenv environments and use pip (or easy_install) for installing your application and any dependencies as well as the pytest package itself. This way you will get an isolated and reproducible environment. Given you have installed virtualenv and execute it from the command line, here is an example session for unix or windows:

virtualenv .   # create a virtualenv directory in the current directory

source bin/activate  # on unix

scripts/activate     # on Windows

We can now install pytest:

pip install pytest

Due to the activate step above the pip will come from the virtualenv directory and install any package into the isolated virtual environment.

Choosing a test layout / import rules

pytest supports two common test layouts:

  • putting tests into an extra directory outside your actual application code, useful if you have many functional tests or for other reasons want to keep tests separate from actual application code (often a good idea):

    setup.py   # your distutils/setuptools Python package metadata
    mypkg/
        __init__.py
        appmodule.py
    tests/
        test_app.py
        ...
    
  • inlining test directories into your application package, useful if you have direct relation between (unit-)test and application modules and want to distribute your tests along with your application:

    setup.py   # your distutils/setuptools Python package metadata
    mypkg/
        __init__.py
        appmodule.py
        ...
        test/
            test_app.py
            ...
    

Important notes relating to both schemes:

  • make sure that “mypkg” is importable, for example by typing once:

    pip install -e .   # install package using setup.py in editable mode
    
  • avoid “__init__.py” files in your test directories. This way your tests can run easily against an installed version of mypkg, independently from the installed package if it contains the tests or not.

  • With inlined tests you might put __init__.py into test directories and make them installable as part of your application. Using the py.test --pyargs mypkg invocation pytest will discover where mypkg is installed and collect tests from there. With the “external” test you can still distribute tests but they will not be installed or become importable.

Typically you can run tests by pointing to test directories or modules:

py.test tests/test_app.py       # for external test dirs
py.test mypkg/test/test_app.py  # for inlined test dirs
py.test mypkg                   # run tests in all below test directories
py.test                         # run all tests below current dir
...

Because of the above editable install mode you can change your source code (both tests and the app) and rerun tests at will. Once you are done with your work, you can use tox to make sure that the package is really correct and tests pass in all required configurations.

Note

You can use Python3 namespace packages (PEP420) for your application but pytest will still perform test package name discovery based on the presence of __init__.py files. If you use one of the two recommended file system layouts above but leave away the __init__.py files from your directories it should just work on Python3.3 and above. From “inlined tests”, however, you will need to use absolute imports for getting at your application code.

Note

If pytest finds a “a/b/test_module.py” test file while recursing into the filesystem it determines the import name as follows:

  • determine basedir: this is the first “upward” (towards the root) directory not containing an __init__.py. If e.g. both a and b contain an __init__.py file then the parent directory of a will become the basedir.
  • perform sys.path.insert(0, basedir) to make the test module importable under the fully qualified import name.
  • import a.b.test_module where the path is determined by converting path separators / into ”.” characters. This means you must follow the convention of having directory and file names map directly to the import names.

The reason for this somewhat evolved importing technique is that in larger projects multiple test modules might import from each other and thus deriving a canonical import name helps to avoid surprises such as a test modules getting imported twice.

Use tox and Continuous Integration servers

If you frequently release code and want to make sure that your actual package passes all tests you may want to look into tox, the virtualenv test automation tool and its pytest support. Tox helps you to setup virtualenv environments with pre-defined dependencies and then executing a pre-configured test command with options. It will run tests against the installed package and not against your source code checkout, helping to detect packaging glitches.

If you want to use Jenkins you can use the --junitxml=PATH option to create a JUnitXML file that Jenkins can pick up and generate reports.

Create a pytest standalone script

If you are a maintainer or application developer and want people who don’t deal with python much to easily run tests you may generate a standalone pytest script:

py.test --genscript=runtests.py

This generates a runtests.py script which is a fully functional basic pytest script, running unchanged under Python2 and Python3. You can tell people to download the script and then e.g. run it like this:

python runtests.py

Integrating with distutils / python setup.py test

You can integrate test runs into your distutils or setuptools based project. Use the genscript method to generate a standalone pytest script:

py.test --genscript=runtests.py

and make this script part of your distribution and then add this to your setup.py file:

from distutils.core import setup, Command
# you can also import from setuptools

class PyTest(Command):
    user_options = []
    def initialize_options(self):
        pass

    def finalize_options(self):
        pass

    def run(self):
        import sys,subprocess
        errno = subprocess.call([sys.executable, 'runtests.py'])
        raise SystemExit(errno)


setup(
    #...,
    cmdclass = {'test': PyTest},
    #...,
)

If you now type:

python setup.py test

this will execute your tests using runtests.py. As this is a standalone version of pytest no prior installation whatsoever is required for calling the test command. You can also pass additional arguments to the subprocess-calls such as your test directory or other options.

Integration with setuptools test commands

Setuptools supports writing our own Test command for invoking pytest. Most often it is better to use tox instead, but here is how you can get started with setuptools integration:

import sys

from setuptools.command.test import test as TestCommand


class PyTest(TestCommand):
    user_options = [('pytest-args=', 'a', "Arguments to pass to py.test")]

    def initialize_options(self):
        TestCommand.initialize_options(self)
        self.pytest_args = []

    def finalize_options(self):
        TestCommand.finalize_options(self)
        self.test_args = []
        self.test_suite = True

    def run_tests(self):
        #import here, cause outside the eggs aren't loaded
        import pytest
        errno = pytest.main(self.pytest_args)
        sys.exit(errno)


setup(
    #...,
    tests_require=['pytest'],
    cmdclass = {'test': PyTest},
    )

Now if you run:

python setup.py test

this will download pytest if needed and then run your tests as you would expect it to. You can pass a single string of arguments using the --pytest-args or -a command-line option. For example:

python setup.py test -a "--durations=5"

is equivalent to running py.test --durations=5.

Conventions for Python test discovery

pytest implements the following standard test discovery:

  • collection starts from the initial command line arguments which may be directories, filenames or test ids.
  • recurse into directories, unless they match norecursedirs
  • test_*.py or *_test.py files, imported by their test package name.
  • Test prefixed test classes (without an __init__ method)
  • test_ prefixed test functions or methods are test items

For examples of how to customize your test discovery Changing standard (Python) test discovery.

Within Python modules, pytest also discovers tests using the standard unittest.TestCase subclassing technique.