Holly Cummins discusses how contract tests combine the lightness of unit tests with the confidence of integration tests, and should be part of your development toolkit.

Introduction to contract-first:

https://www.redhat.com/en/blog/achieving-promise-microservices-one-contract-time

A tutorial on doing contract-first using an OpenAPI approach:

https://appdev.consulting.redhat.com/tracks/contract-first/

The documentation for the JVM binding for Pact:

https://docs.pact.io/implementation_guides/jvm

The Pact Quarkus extension:

https://github.com/quarkiverse/quarkus-pact

The sample code:

https://github.com/holly-cummins/pact-quarkus-sweater-demo