Python version of Pact. Enables consumer driven contract testing, providing a mock service and DSL for the consumer project, and interaction playback and verification for the service provider project. Currently supports version 2 of the Pact specification.
For more information about what Pact is, and how it can help you test your code more efficiently, check out the Pact documentation.
pip install pact-python
Creating a complete contract is a two step process:
- Create a test on the consumer side that declares the expectations it has of the provider
- Create a provider state that allows the contract to pass when replayed against the provider
If we have a method that communicates with one of our external services, which we'll call
Provider, and our product, Consumer is hitting an endpoint on Provider at
/users/<user> to get information about a particular user.
If the code to fetch a user looked like this:
import requests
def user(user_name):
"""Fetch a user object by user_name from the server."""
uri = 'http://localhost:1234/users/' + user_name
return requests.get(uri).json()Then Consumer's contract test might look something like this:
import atexit
import unittest
from pact import Consumer, Provider
pact = Consumer('Consumer').has_pact_with(Provider('Provider'))
pact.start_service()
atexit.register(pact.stop_service)
class GetUserInfoContract(unittest.TestCase):
def test_get_user(self):
expected = {
'username': 'UserA',
'id': 123,
'groups': ['Editors']
}
(pact
.given('UserA exists and is not an administrator')
.upon_receiving('a request for UserA')
.with_request('get', '/users/UserA')
.will_respond_with(200, body=expected))
with pact:
result = user('UserA')
self.assertEqual(result, expected)This does a few important things:
- Defines the Consumer and Provider objects that describe our product and our service under test
- Uses
givento define the setup criteria for the ProviderUserA exists and is not an administrator - Defines what the request that is expected to be made by the consumer will contain
- Defines how the server is expected to respond
Using the Pact object as a context manager, we call our method under test
which will then communicate with the Pact mock service. The mock service will respond with
the items we defined, allowing us to assert that the method processed the response and
returned the expected value. If you want more control over when the mock service is
configured and the interactions verified, use the setup and verify methods, respectively:
(pact
.given('UserA exists and is not an administrator')
.upon_receiving('a request for UserA')
.with_request('get', '/users/UserA')
.will_respond_with(200, body=expected))
pact.setup()
# Some additional steps before running the code under test
result = user('UserA')
# Some additional steps before verifying all interactions have occurred
pact.verify()When defining the expected HTTP request that your code is expected to make you can specify the method, path, body, headers, and query:
pact.with_request(
method='GET',
path='/api/v1/my-resources/',
query={'search': 'example'}
)query is used to specify URL query parameters, so the above example expects
a request made to /api/v1/my-resources/?search=example.
pact.with_request(
method='POST',
path='/api/v1/my-resources/123',
body={'user_ids': [1, 2, 3]},
headers={'Content-Type': 'application/json'},
)You can define exact values for your expected request like the examples above, or you can use the matchers defined later to assist in handling values that are variable.
The default hostname and port for the Pact mock service will be
localhost:1234 but you can adjust this during Pact creation:
from pact import Consumer, Provider
pact = Consumer('Consumer').has_pact_with(
Provider('Provider'), host_name='mockservice', port=8080)This can be useful if you need to run to create more than one Pact for your test
because your code interacts with two different services. It is important to note
that the code you are testing with this contract must contact the mock service.
So in this example, the user method could accept an argument to specify the
location of the server, or retrieve it from an environment variable so you can
change its URI during the test.
The mock service offers you several important features when building your contracts:
- It provides a real HTTP server that your code can contact during the test and provides the responses you defined.
- You provide it with the expectations for the request your code will make and it will assert the contents of the actual requests made based on your expectations.
- If a request is made that does not match one you defined or if a request from your code is missing it will return an error with details.
- Finally, it will record your contracts as a JSON file that you can store in your repository or publish to a Pact broker.
The above test works great if that user information is always static, but what happens if the user has a last updated field that is set to the current time every time the object is modified? To handle variable data and make your tests more robust, there are 3 helpful matchers:
Asserts the value should match the given regular expression. You could use this to expect a timestamp with a particular format in the request or response where you know you need a particular format, but are unconcerned about the exact date:
from pact import Term
...
body = {
'username': 'UserA',
'last_modified': Term('\d+-\d+-\d+T\d+:\d+:\d+', '2016-12-15T20:16:01')
}
(pact
.given('UserA exists and is not an administrator')
.upon_receiving('a request for UserA')
.with_request('get', '/users/UserA/info')
.will_respond_with(200, body=body))When you run the tests for the consumer, the mock service will return the value you provided
as generate, in this case 2016-12-15T20:16:01. When the contract is verified on the
provider, the regex will be used to search the response from the real provider service
and the test will be considered successful if the regex finds a match in the response.
Asserts the element's type matches the matcher. For example:
from pact import Like
Like(123) # Matches if the value is an integer
Like('hello world') # Matches if the value is a string
Like(3.14) # Matches if the value is a floatThe argument supplied to Like will be what the mock service responds with.
When a dictionary is used as an argument for Like, all the child objects (and their child objects etc.) will be matched according to their types, unless you use a more specific matcher like a Term.
from pact import Like, Term
Like({
'username': Term('[a-zA-Z]+', 'username'),
'id': 123, # integer
'confirmed': False, # boolean
'address': { # dictionary
'street': '200 Bourke St' # string
}
})Asserts the value is an array type that consists of elements like the one passed in. It can be used to assert simple arrays:
from pact import EachLike
EachLike(1) # All items are integers
EachLike('hello') # All items are stringsOr other matchers can be nested inside to assert more complex objects:
from pact import EachLike, Term
EachLike({
'username': Term('[a-zA-Z]+', 'username'),
'id': 123,
'groups': EachLike('administrators')
})Note, you do not need to specify everything that will be returned from the Provider in a JSON response, any extra data that is received will be ignored and the tests will still pass.
Note, to get the generated values from an object that can contain matchers like Term, Like, EachLike, etc. for assertion in self.assertEqual(result, expected) you may need to use get_generated_values() helper function:
from pact.matchers import get_generated_values
self.assertEqual(result, get_generated_values(expected))For more information see Matching
In addition to writing Pacts for Python consumers, you can also verify those Pacts
against a provider of any language. After installing pact-python a pact-verifier
application should be available. To get details about its use you can call it with the
help argument:
pact-verifier --helpThe simplest example is verifying a server with locally stored Pact files and no provider states:
pact-verifier --provider-base-url=http://localhost:8080 --pact-url=./pacts/consumer-provider.jsonWhich will immediately invoke the Pact verifier, making HTTP requests to the server located
at http://localhost:8080 based on the Pacts in ./pacts/consumer-provider.json and
reporting the results.
There are several options for configuring how the Pacts are verified:
Required. Defines the URL of the server to make requests to when verifying the Pacts.
Required if --pact-urls not specified. The location of a Pact file you want to verify. This can be a URL to a Pact Broker or a local path, to provide multiple files, specify multiple arguments.
pact-verifier --provider-base-url=http://localhost:8080 --pact-url=./pacts/one.json --pact-url=./pacts/two.json
Required if --pact-url not specified. The location of the Pact files you want to verify. This can be a URL to a Pact Broker or one or more local paths, separated by a comma.
DEPRECATED AFTER v 0.6.0. The URL where your provider application will produce the list of available provider states. The verifier calls this URL to ensure the Pacts specify valid states before making the HTTP requests.
The URL which should be called to setup a specific provider state before a Pact is verified. This URL will be called with a POST request, and the JSON body {consumer: 'Consumer name', state: 'a thing exists'}.
The username to use when contacting the Pact Broker.
The password to use when contacting the Pact Broker. You can also specify this value
as the environment variable PACT_BROKER_PASSWORD.
In many cases, your contracts will need very specific data to exist on the provider to pass successfully. If you are fetching a user profile, that user needs to exist, if querying a list of records, one or more records needs to exist. To support decoupling the testing of the consumer and provider, Pact offers the idea of provider states to communicate from the consumer what data should exist on the provider.
When setting up the testing of a provider you will also need to setup the management of
these provider states. The Pact verifier does this by making additional HTTP requests to
the --provider-states-setup-url you provide. This URL could be
on the provider application or a separate one. Some strategies for managing state include:
- Having endpoints in your application that are not active in production that create and delete your datastore state
- A separate application that has access to the same datastore to create and delete, like a separate App Engine module or Docker container pointing to the same datastore
- A standalone application that can start and stop the other server with different datastore states
For more information about provider states, refer to the Pact documentation on Provider States.
Please read CONTRIBUTING.md
To setup a development environment:
- If you want to run tests for all Python versions, install 2.7, 3.3, 3.4, 3.5, and 3.6 from source or using a tool like pyenv
- Its recommended to create a Python virtualenv for the project
The setup the environment, run tests, and package the application, run:
make release
If you are just interested in packaging pact-python so you can install it using pip:
make package
This creates a dist/pact-python-N.N.N.tar.gz file, where the Ns are the current version.
From there you can use pip to install it:
pip install ./dist/pact-python-N.N.N.tar.gz
This project has unit and end to end tests, which can both be run from make:
Unit: make test
End to end: make e2e
Join us in slack:
or
- Twitter: [@pact_up]
- Stack Overflow: stackoverflow.com/questions/tagged/pact