Part seventeen of a series of posts about automated testing.

Continuing the example from yesterday’s post, we would like to create some form of tests to catch incompatible changes in the geolocation service, which would potentially break the navigation service.

Suppose the response from the geolocation service is JSON:

"id": "123",
"lat": "51.2",
"lon": "-0.83",
"name": "Fleet",
"county": "Hampshire",
"country": "UK"

Santa’s navigation service, however, uses only the latitude and longitude fields. The navigation service could create a “contract” between itself and the geolocation service, that required the latter to provide the lat/lon fields. The geolocation service could then run these as regression tests on every build.

This way, if a change to geolocation broke functionality that the navigation service relied upon, it would be flagged up before release.

These contract tests will have fewer moving parts than full end-to-end tests, so will be faster and more reliable.

There is software available that implements this kind of testing framework - Pact is one option, and it has native ports to many languages (plus a docker-based solution if there is no native port).

Further reading