What is Contract Testing?

Contract testing is a technique for verifying the interactions between different software systems, particularly in microservice architectures. Instead of end-to-end testing, which can be brittle and slow, contract testing focuses on validating that each service adheres to the agreed-upon contracts (e.g., API schemas, message formats) defined between services. This involves verifying that a 'consumer' of a service can process the data it receives from the 'provider' as expected, and that the 'provider' can fulfill the consumer's requests according to the contract. This helps ensure that services can evolve independently without breaking existing integrations.