Sample project to set up contract testing for a smaple application using pact, python implementation. As a refference I use pact-python official repo example.

Setup Python Environment

To install working environment for Python and the project dependencies run the script

./setup.sh

Please, follow instructions printed by the script by the end of execution.

Sample Provider Service

The sample service app/app.py translates numbers to different languages. It has a HTTP API. The only endpoint GET /translate/1 translates prime numbers to various languages 200 OK {"ua": "Один", "en": "One"}. When there is no translation for a given number, it will respond with 404 Not found.

To run the service on http://localhost:5000/:

python app/app.py

Contract tests

Install tools

When the python environment is ready install (1) pact and (2) pact mock service (ruby is required). Mock service is needed to run the contract tests.

Install pact-python:

pip install pact-python

Install pact mock service:

gem install pact-mock_service

Start the mock service on http://localhost:1234:

pact-mock-service start

Create and Run

In this example I use unittest to create the contract tests contract_tests/translate_service_test.py. given is a specific provider state. The state should be implemented later by Provider. For example, if your test requires some data in the service provider data store.

Execute the contract tests:

python -m unittest contract_tests/translate_service_test.py

The test will run against the pact mock service, which verifies if all requests in the tests were triggered. If successful, pact mock service will generate a pact file in JSON format pacts/translator_translate-service.json. The location of the dir where the pacts should be stored you setup in the test:

from pact import Consumer, Provider
pact = Consumer('Translator').has_pact_with(Provider('Translate Service'), pact_dir='./pacts')

Provider

Implement Provider State

pact-verifier is installed with pact-python. It is a utility to verify the pact instructions against a real service provider. It needs to know where are provider states implemented --provider-states-url and --provider-states-setup-url. When pact-verifier reads the instructions and finds a providerState it makes a call to the URL provided in --provider-states-setup-url with a body:

{consumer: <consumer_name>, states: [<state_name>]}

For some reason, pact-verifier requires --provider-states-url to be specified but doesn't use it.

I implemented provider states inside the sample application app/app.py. The provider state name can be passed by pact-verifier to POST /_pact/provider_states/ with expected Body: {consumer: ‘Translator’, states: [‘translation for number 1’]} and the state will be executed to set up the state of the service.

Verify a pact

To verify a pact instructions run:

pact-verifier --provider-base-url=http://localhost:5000/ --pact-url=pacts/translator-translate_service.json --provider-states-url=http://localhost:5000/_pact/provider_states/all --provider-states-setup-url=http://localhost:5000/_pact/provider_states

At the end, you should see a report printed to the command line output.