Contract testing is a testing methodology based on adhering to API service contracts. An API service contract is the interface documentation of the code spec and business login. It details how the code is supposed to run and what it is supposed to do. In other words, contract tests should pass the expected scenario detailed in the contract.

Contract testing is a good solution for microservices testing. Here are five reasons why:

1. Development Speed

A microservices architecture requires developers to quickly understand different parts of the code that are not connected. For example, when they are developing a new feature on top of an existing service. But documentation is often outdated, and team members are not always available to answer questions. Contracts detail API specs and logic so that developers can quickly understand new code and develop on top of it. This replaces lengthy processes, endless back and forths and time spent learning the code.
Bonus: You can also easily test your new enhancements against older versions for backward compatibility, since they are kept handy through contracts.

2. Testing Scalability

Service contracts can be created and tested for each and every service, separately. Today, few solutions enable testing of each service. End-to-end testing of a microservices architecture hinders agility and often leads to unreliable results . Implementing contracts and testing them in a continuous manner enables test scaling and reduced software regressions.

3. Quicker Bug Fixes

The contract specifies the intended code behavior. This makes it easier to identify when it is not working, and to come up with different testing scripts for additional scenarios. Knowing what the code's intended behavior helps identify bugs, fix them quicker, and ultimately deploy to production sooner. This enables agile development, the core of microservices development.

4. Reduced Infrastructure Costs

Developers must deploy a dev environment in the cloud when making code changes to a microservices architecture. This ensures they do not clash with the development of other services. But dev environments are costly, and can be forgotten. A dev can easily forget to descale a cluster or take an environment down.
Implementing contracts enables developers to develop and execute their code with lightweight mocks, directly on their laptops. This reduces costs, and also increases productivity.

5. Ownership and Accountability

Contract testing empowers extreme code ownership from the publishers. The contract reflects their professionalism via their contract (check out Stripe API Docs for an example). Therefore, they will surely invest in it and in the code. A good contract also reduces the number of questions they'll get, translating into more coding or coffee time. It's a win-win for everyone.

Contract testing is a valuable solution for testing microservices. However, it can be a complicated process. UP9 enables developers to effortlessly create automated contract tests for microservices. Here's how:


UP9 is a microservice testing platform for Cloud Native systems that can scale across any number of services. UP9 helps developers prevent software regressions and increase engineering productivity through effortless testing and instant virtualization.

  • Understand how services interact with each other with automatic contract discovery.
  • Ensure system-wide contract adherence with tests that write themselves.
  • Start testing early with test environments as code, automatically mocking all service dependencies.

UP9 offloads the microservice testing workload from developers, giving them precious time back.

You can sign up now for free!