Contract testing

Contract testing

When working with APIs between teams or external partners, it is especially important that the format of requests and responses remains predictable. Contract testing allows you to verify that both parties - the client and the server - agree to the exchange structure and do not violate it during updates.

We implement contract tests that automatically check API compliance with documentation or consumer expectations - before going into production.

What is an API contract

A contract is an agreement that defines:

• which fields contain the request and response
• what data formats are allowed
• which status codes are returned
• what mandatory parameters are required

Contract violation = potential customer or service failure.

How does it work

Party	What is being tested
Provider (API)	API must meet client expectations for response structure
Customer	The customer expects a specific schema - the test verifies that it is met
Bidirectional	Two-way testing: both client and server agree to contract

Tools used: Pact, Spring Cloud Contract, Dredd, Postman Contract Tests.

Benefits of contract testing

Identification of non-conformities prior to depletion
Protect against "silent" changes that break customers
Safely update API versions
Increase trust between development teams
Logging contract change history

How we implement

Define OpenAPI/Pact contracts
CI integration with automatic test runs at each commit
Visualization and history of contract changes
Staging/production
Publishing Contracts for External Integrators

Where especially important

Shared responsibility microservices
Platforms with external B2B integrations
Working on APIs with Multiple Independent Commands
Critical systems where error is unacceptable (finance, public services)

Contract testing is a reliable bridge between the server and the client. We will help you build a process in which no update disrupts integration and does not bring unexpected bugs.