Pact Test for Python

This repository contains a Python implementation for Pact. Pact is a specification for Consumer Driven Contracts Testing. For further information about Pact project, contracts testing, pros and cons and useful resources please refer to the Pact website.

There are two phases in Consumer Driven Contracts Testing: a Consumer sets up a contract (it's consumer driven after all!), and a Provider honours it. But, before that...

Installation

Pact Test is distributed through PyPi so it can be easily included in the requirements.txt file or normally installed with pip:

$ pip install pact-test

Providers Tests (Set the Contracts)

Consumers run Provider Tests to create pacts and establish a contract between them and service providers. An example of a Python client using pact test is available at here. Consumers define all the interactions with their providers in the following way:

@service_consumer('PythonEats')
@has_pact_with('PyzzaHut')
class PyzzaHutTest(ServiceProviderTest):

    @given('some pizzas exist')
    @upon_receiving('a request for a pepperoni pizza')
    @with_request({'method': 'get', 'path': '/pizzas/pepperoni/'})
    @will_respond_with({'status': 200, 'body': {'id': 42, 'type': 'pepperoni'}})
    def test_get_pepperoni_pizza(self):
        pizza = get_pizza('pepperoni')
        assert pizza['id'] == 42
        assert pizza['type'] == 'pepperoni'

This test verifies, against a mock server, the expected interaction and creates a JSON file (the pact) that will be stored locally and also sent to the Pact Broker, if available. It is possible to define multiple tests for the same state in order to verify all the scenarios of interest, For example, we can test an unhappy 404 situation:

@given('some pizzas exist')
@upon_receiving('a request for an hawaiian pizza')
@with_request({'method': 'get', 'path': '/pizzas/hawaiian/'})
@will_respond_with({'status': 404, 'body': {'message': 'we do not serve pineapple with pizza'}})
def test_get_hawaiian_pizza(self):
    pizza = get_pizza('hawaiian')
    assert pizza.status_code == 404
    assert pizza.json()['message'] == 'we do not serve pineapple with pizza'

Consumers Tests (Honour Your Contracts)

Providers run Consumer Tests to verify that they are honouring their pacts with the consumers. There are few examples of an hypothetical restaurant service implemented with the most popular Python web frameworks:

• Djanjo (TODO)
• Flask
• Pyramid

There are few things required to setup and run consumer tests.

Pact Helper

This helper class is used by Pact Test to start and stop the web-app before and after the test. It also defines the ports and endpoint to be used by the test. The following is an example of Pact Helper:

class RestaurantPactHelper(PactHelper):
    process = None

    def setup(self):
        self.process = subprocess.Popen('gunicorn start:app -w 3 -b :8080 --log-level error', shell=True)

    def tear_down(self):
        self.process.kill()

There are few rules for the helper:

• it must extend PactHelper class from pact_test
• it must define a setup method
• it must define a tear_down method

It is also possible to override default url (localhost) and port (9999):

class RestaurantPactHelper(PactHelper):
    test_url = '0.0.0.0'
    test_port = 5000

States

When a consumer sets a pact, it defines certain states. States are basically pre-requisites to your test. Before honouring the pacts, a provider needs to define such states. For example:

@honours_pact_with('UberEats')
@pact_uri('http://Kalimaha.github.io/src/pacts/pact.json')
class UberEats(ServiceConsumerTest):

    @state('some menu items exist')
    def test_get_menu_items(self):
        DB.save(MenuItem('spam'))
        DB.save(MenuItem('eggs'))

In this example, the provider stores some test data in its DB in order to make the system ready to receive mock calls from the consumer and therefore verify the pact.

Configuration

The default configuration of Pact Test assumes the following values:

• consumer_tests_path: tests/service_consumers
• provider_tests_path: tests/service_providers
• pact_broker_uri: None

It is possible to override such values by creating a file named .pact.json in the project's root. The following is an example of a valid configuration file:

{
  "consumer_tests_path": "mypath/mytests",
  "provider_tests_path": "mypath/mytests",
  "pact_broker_uri": "http://example.com/"
}

All fields are optional: only specified fields will override default configuration values.

Development

Setup

python3 setup.py install

Test

It is possible to run the tests locally with Docker through the following command:

$ ./bin/test

By default this command tests the library against Python 3.6. It is possible to specify the Python version as follows:

$ ./bin/test <ENV>

Available values for ENV are: py27, py33, py34, py35 py36, py37 and py38. It is also possible to test all the versions at once with:

$ ./bin/test all

Upload New Version

$ python3 setup.py sdist upload

With Python Wheels:

$ python3 setup.py sdist bdist_wheel
$ twine upload dist/*