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