py.test plugin for functional testing with Docker

It’s very useful to run functional tests in a clean environment, like a fresh Docker container, and I wrote about this before, and now it was formalized in a simple py.test plugin — pytest-docker-pexpect.

It provides few useful fixtures:

spawnu – pexpect.spawnu object attached to a container, it can be used to interact with apps inside the container, read more;
TIMEOUT – a special object, that can be used in assertions those checks output;
run_without_docker – indicates that tests running without Docker, when py.test called with --run-without-docker.

And some marks:

skip_without_docker – skips test when without Docker;
once_without_docker – runs parametrized test only with a first set of params when without Docker.

It’s easier to show it in examples. So, first of all, just test some app --version argument inside an Ubuntu container:

import pytest


@pytest.fixture
def ubuntu(spawnu):
    # Get `spawnu` attached to ubuntu container with installed python and
    # where bash ran
    proc = spawnu(u'example/ubuntu',
                  u'''FROM ubuntu:latest
                      RUN apt-get update
                      RUN apt-get install python python-dev python-pip''',
                  u'bash')
    # Sources root is available in `/src`
    proc.sendline(u'pip install /src')
    return proc


def test_version(ubuntu, TIMEOUT):
    ubuntu.sendline(u'app --version')
    # Asserts that `The App 2.9.1` came before timeout,
    # when timeout came first, `expect` returns 0, when app version - 1
    assert ubuntu.expect([TIMEOUT, u'The App 2.9.1'])

Looks simple. But sometimes we need to run tests in different environments, for example — with different Python versions. It can be easily done by just changing ubuntu fixture:

@pytest.fixture(params=[2, 3])
def ubuntu(request, spawnu):
    python_version = request.param
    # Get `spawnu` attached to ubuntu container with installed python and
    # where bash ran
    dockerfile = u'''
        FROM ubuntu:latest
        RUN apt-get update
        RUN apt-get install python{version} python{version}-dev python{version}-pip
    '''.format(version=python_version)
    proc = spawnu(u'example/ubuntu', dockerfile, u'bash')
    # Your source root is available in `/src`
    proc.sendline(u'pip{} install /src'.format(python_version))
    return proc

And sometimes we need to run tests in Docker-less environment, for example — in Travis CI container-based infrastructure. So here’s where --run-without-docker argument comes handy. But we don’t need to run tests for more than one environment in a single Travis CI run, and we don’t need to make some installation steps. So there’s place for once_without_docker mark and run_without_docker fixture, test with them will be:

import pytest


@pytest.fixture(params=[2, 3])
def ubuntu(request, spawnu, run_without_docker):
    python_version = request.param
    # Get `spawnu` attached to ubuntu container with installed python and
    # where bash ran
    dockerfile = u'''
        FROM ubuntu:latest
        RUN apt-get update
        RUN apt-get install python{version} python{version}-dev python{version}-pip
    '''.format(version=python_version)
    proc = spawnu(u'example/ubuntu', dockerfile, u'bash')
    # It's already installed if we run without Docker:
    if not run_without_docker:
        # Your source root is available in `/src`
        proc.sendline(u'pip{} install /src'.format(python_version))
    return proc


@pytest.mark.once_without_docker
def test_version(ubuntu, TIMEOUT):
    ubuntu.sendline(u'app --version')
    # Asserts that `The App 2.9.1` came before timeout,
    # when timeout came first, `expect` returns 0, when app version - 1
    assert ubuntu.expect([TIMEOUT, u'The App 2.9.1'])

Another often requirement — skip some tests without docker, some destructive tests. It can be done with skip_without_docker mark:

@pytest.mark.skip_without_docker
def test_broke_config(ubuntu, TIMEOUT):
    ubuntu.sendline(u'{invalid} > ~/.app/config.json')
    ubuntu.sendline(u'app')
    assert ubuntu.expect([TIMEOUT, u'Config was broken!'])

Source code of the plugin.