By combining unit, integration and component testing, we are able to achieve high coverage of the modules that make up a microservice and can be sure that the microservice correctly implements the required business logic.

Yet, in all but the simplest use cases, business value is not achieved unless many microservices work together to fulfil larger business processes. Within this testing scheme, there are still no tests that ensure external dependencies meet the contract expected of them or that our collection of microservices collaborate correctly to provide end-to-end business flows.

Contract testing of external dependencies and more coarse grained end-to-end testing of the whole system help to provide this.