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snapshottest

Snapshot Testing utils for Python 📸

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Snapshot testing is a way to test your APIs without writing actual test cases.

  1. A snapshot is a single state of your API, saved in a file.
  2. You have a set of snapshots for your API endpoints.
  3. Once you add a new feature, you can generate automatically new snapshots for the updated API.

Installation

$ pip install snapshottest

Usage with unittest/nose

from snapshottest import TestCase

class APITestCase(TestCase):
    def test_api_me(self):
        """Testing the API for /me"""
        my_api_response = api.client.get('/me')
        self.assertMatchSnapshot(my_api_response)

        # Set custom snapshot name: `gpg_response`
        my_gpg_response = api.client.get('/me?gpg_key')
        self.assertMatchSnapshot(my_gpg_response, 'gpg_response')

If you want to update the snapshots automatically you can use the nosetests --snapshot-update.

Check the Unittest example.

Usage with pytest

def test_mything(snapshot):
    """Testing the API for /me"""
    my_api_response = api.client.get('/me')
    snapshot.assert_match(my_api_response)

    # Set custom snapshot name: `gpg_response`
    my_gpg_response = api.client.get('/me?gpg_key')
    snapshot.assert_match(my_gpg_response, 'gpg_response')

If you want to update the snapshots automatically you can use the --snapshot-update config.

Check the Pytest example.

Usage with django

Add to your settings:

TEST_RUNNER = 'snapshottest.django.TestRunner'

To create your snapshottest:

from snapshottest.django import TestCase

class APITestCase(TestCase):
    def test_api_me(self):
        """Testing the API for /me"""
        my_api_response = api.client.get('/me')
        self.assertMatchSnapshot(my_api_response)

If you want to update the snapshots automatically you can use the python manage.py test --snapshot-update. Check the Django example.

Disabling terminal colors

Set the environment variable ANSI_COLORS_DISABLED (to any value), e.g.

ANSI_COLORS_DISABLED=1 pytest

Contributing

After cloning this repo and configuring a virtualenv for snapshottest (optional, but highly recommended), ensure dependencies are installed by running:

make develop

After developing, ensure your code is formatted properly by running:

make format-fix

and then run the full test suite with:

make lint
# and
make test

To test locally on all supported Python versions, you can use tox:

pip install tox  # (if you haven't before)
tox

Notes

This package is heavily inspired in jest snapshot testing.

Reasons to use this package

Most of this content is taken from the Jest snapshot blogpost.

We want to make it as frictionless as possible to write good tests that are useful. We observed that when engineers are provided with ready-to-use tools, they end up writing more tests, which in turn results in stable and healthy code bases.

However engineers frequently spend more time writing a test than the component itself. As a result many people stopped writing tests altogether which eventually led to instabilities.

A typical snapshot test case for a mobile app renders a UI component, takes a screenshot, then compares it to a reference image stored alongside the test. The test will fail if the two images do not match: either the change is unexpected, or the screenshot needs to be updated to the new version of the UI component.

Snapshot Testing with SnapshotTest

A similar approach can be taken when it comes to testing your APIs. Instead of rendering the graphical UI, which would require building the entire app, you can use a test renderer to quickly generate a serializable value for your API response.

License

MIT License

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