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pytest-docker-compose

https://circleci.com/gh/pytest-docker-compose/pytest-docker-compose/tree/master.svg?style=svg

This package contains a pytest plugin for integrating Docker Compose into your automated integration tests.

Given a path to a docker-compose.yml file, it will automatically build the project at the start of the test run, bring the containers up before each test starts, and tear them down after each test ends.

Dependencies

Make sure you have Docker installed.

This plugin is automatically tested against the following software:

  • Python 3.5 and 3.6.
  • pytest 3, 4 and 5.

Note

This plugin is not compatible with Python 2.

Locally I tested it successfully against Python 3.7 as well but 3.7 proved hard to integrate into circleCI so it's not officially supported.

Installation

Install the plugin using pip:

> pip install pytest-docker-compose

Usage

For performance reasons, the plugin is not enabled by default, so you must activate it manually in the tests that use it:

pytest_plugins = ["docker_compose"]

See Installing and Using Plugins for more information.

To interact with Docker containers in your tests, use the following fixtures, these fixtures tell docker-compose to start all the services and then they can fetch the associated containers for use in a test:

function_scoped_container_getter

An object that fetches containers of the Docker compose.container.Container objects running during the test. The containers are fetched using function_scoped_container_getter.get('service_name') These containers each have an extra attribute called network_info added to them. This attribute has a list of pytest_docker_compose.NetworkInfo objects.

This information can be used to configure API clients and other objects that will connect to services exposed by the Docker containers in your tests.

NetworkInfo is a container with the following fields:

  • container_port: The port (and usually also protocol name) exposed internally to the container. You can use this value to find the correct port for your test, when the container exposes multiple ports.
  • hostname: The hostname (usually "localhost") to use when connecting to the service from the host.
  • host_port: The port number to use when connecting to the service from the host.
docker_project
The compose.project.Project object that the containers are built from. This fixture is generally only used internally by the plugin.

To use the following fixtures please read Use wider scoped fixtures.

class_scoped_container_getter
Similar to function_scoped_container_getter just with a wider scope.
module_scoped_container_getter
Similar to function_scoped_container_getter just with a wider scope.
session_scoped_container_getter
Similar to function_scoped_container_getter just with a wider scope.

Waiting for Services to Come Online

The fixtures called 'scope'_scoped_container_getter will wait until every container is up before handing control over to the test.

However, just because a container is up does not mean that the services running on it are ready to accept incoming requests yet!

If your tests need to wait for a particular condition (for example, to wait for an HTTP health check endpoint to send back a 200 response), make sure that your fixtures account for this.

Here's an example of a fixture called wait_for_api that waits for an HTTP service to come online before a test called test_read_and_write can run.

import pytest
import requests
from urllib.parse import urljoin
from urllib3.util.retry import Retry
from requests.adapters import HTTPAdapter

pytest_plugins = ["docker_compose"]

# Invoking this fixture: 'function_scoped_container_getter' starts all services
@pytest.fixture(scope="function")
def wait_for_api(function_scoped_container_getter):
    """Wait for the api from my_api_service to become responsive"""
    request_session = requests.Session()
    retries = Retry(total=5,
                    backoff_factor=0.1,
                    status_forcelist=[500, 502, 503, 504])
    request_session.mount('http://', HTTPAdapter(max_retries=retries))

    service = function_scoped_container_getter.get("my_api_service").network_info[0]
    api_url = "http://%s:%s/" % (service.hostname, service.host_port)
    assert request_session.get(api_url)
    return request_session, api_url


def test_read_and_write(wait_for_api):
    """The Api is now verified good to go and tests can interact with it"""
    request_session, api_url = wait_for_api
    data_string = 'some_data'
    request_session.put('%sitems/2?data_string=%s' % (api_url, data_string))
    item = request_session.get(urljoin(api_url, 'items/2')).json()
    assert item['data'] == data_string
    request_session.delete(urljoin(api_url, 'items/2'))

Use wider scoped fixtures

The function_scoped_container_getter fixture uses "function" scope, meaning that all of the containers are torn down after each individual test.

This is done so that every test gets to run in a "clean" environment. However, this can potentially make a test suite take a very long time to complete.

There are two options to make containers persist beyond a single test. The best way is to use the fixtures that are explicitly scoped to different scopes. There are three additional fixtures for this purpose: class_scoped_container_getter, module_scoped_container_getter and session_scoped_container_getter. Notice that you need to be careful when using these! There are two main caveats to keep in mind:

  1. Manage your scope correctly, using 'module' scope and 'function' scope in one single file will throw an error! This is because the module scoped fixture will spin up the containers and then the function scoped fixture will try to spin up the containers again. Docker compose does not allow you to spin up containers twice.
  2. Clean up your environment after each test. Because the containers are not restarted their environments can carry the information from previous tests. Therefore you need to be very carefull when designing your tests such that they leave the containers in the same state that it started in or you might run into difficult to understand behaviour.

A second method to make containers persist beyond a single test is to supply the --use-running-containers flag to pytest like so:

pytest --use-running-containers

With this flag, pytest-docker-compose checks that all containers are running during the project creation. If they are not running a warning is given and they are spun up anyways. They are then used for all the tests and NOT TORE DOWN afterwards.

This mode is best used in combination with the '--docker-compose-no-build' flag since the newly build containers won't be used anyways. like so:

pytest --docker-compose-no-build --use-running-containers

It is off course possible to add these options to pytest.ini.

Notice that for this mode the scoping of the fixtures becomes less important since the containers are fully persistent throughout all tests. I only recommend using this if your network takes excessively long to spin up/tear down. It should really be a last resort and you should probably look into speeding up your network instead of using this.

Running Integration Tests

Use pytest to run your tests as normal:

pytest

By default, this will look for a docker-compose.yml file in the current working directory. You can specify a different file via the --docker-compose option:

pytest --docker-compose=/path/to/docker-compose.yml

Docker compose allows for specifying multiple compose files as described in the docs here. To specify more than one compose file, separate them with a ,:

pytest --docker-compose=/path/to/docker-compose.yml,/another/docker-compose.yml,/third/docker-compose.yml

Tip

Alternatively, you can specify this option in your pytest.ini file:

[pytest]
addopts = --docker-compose=/path/to/docker-compose.yml

The option will be ignored for tests that do not use this plugin.

See Configuration Options for more information on using configuration files to modify pytest behavior.

Remove volumes after tests

There is another configuration option that will delete the volumes of containers after running.

pytest --docker-compose-remove-volumes

This option will be ignored if the plugin is not used. Again, this option can also be added to the pytest.ini file.

For more examples on how to use this plugin look at the testing suite of this plugin itself! It will give you some examples for configuring pytest.ini and how to use the different fixtures to run docker containers.