Cloud, Security & Operations
API Testing
Testing APIs directly for correct responses, business rules, error handling, security checks, contract compatibility and performance, using Postman, REST Assured, Karate or Pact in automated pipelines.
Capability overview
What api testing involves
APIs carry the business logic behind web apps, mobile apps and partner integrations, so testing them directly finds defects faster and more precisely than testing through a user interface. API tests run in seconds, are less brittle than UI automation and can check conditions that are hard to reach through screens.
We test REST, GraphQL and SOAP APIs for response correctness, schema compliance, status codes, business rules, pagination, filtering, idempotency and error handling. Consumer-driven contract testing with Pact protects consumers from breaking changes, and negative tests check that invalid tokens and unauthorised object access are rejected. API suites also double as living documentation, showing exactly how each endpoint is expected to behave for typical requests, edge cases and errors.
What is included
API test coverage
Functional API tests
Requests validated for correct data, calculations, state changes and status codes across typical and edge scenarios.
Schema and contract tests
Responses checked against OpenAPI specifications and consumer contracts to detect breaking changes early.
Negative and boundary tests
Invalid payloads, missing fields, oversized inputs and wrong content types tested for safe handling.
Authorisation checks
Token expiry, scopes and access to other users' or tenants' objects verified to be blocked.
API performance baselines
Response times measured for key endpoints so regressions are caught in pipelines.
How we work
How we deliver api testing
API inventory
Endpoints, specifications, authentication methods and consumers documented.
Test design
Scenarios derived from specifications, business rules and known consumer usage.
Automation build
Test collections or code-based suites built with reusable authentication and data setup.
Pipeline integration
API tests run on every build, with contract checks before deployment.
Coverage review
Endpoint and scenario coverage reviewed as APIs change.
Related capabilities
Related capabilities in Quality Engineering & Testing
Integration Testing
Testing how modules, services and external systems work together, including data flows between applications, message queues, third-party APIs and batch interfaces, using service virtualisation where partners are unavailable.
Performance Testing
Measuring and improving how fast and efficiently applications respond, from backend response times and database queries to front-end rendering, with bottleneck analysis that explains why systems are slow.
Load & Stress Testing
Simulating peak and extreme traffic to confirm systems handle sale days, admission results, tax deadlines and campaign launches, and to find breaking points before real users do.
Security Testing
Security checks built into the QA cycle for every release, including automated SAST, dependency and DAST scans, authorisation test cases and security regression tests, complementing periodic penetration tests.
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Questions & answers
Questions about API Testing
Cannot find what you need? Our team responds to technical and commercial questions within one business day.
Ask a questionPostman suits quick collaboration and moderate automation, REST Assured and Karate suit code-based suites in Java ecosystems, and Pact suits contract testing between services. Many teams use more than one.
A method where API consumers define the interactions they depend on and providers verify those contracts automatically, so incompatible changes are caught before deployment.
It reduces the amount of UI testing needed. A small number of end-to-end UI tests still confirm that the interface and APIs work together for critical journeys.
By number of endpoints and scenario complexity for fixed-scope suites, or through automation engineers billed monthly.
Next step
Discuss api testing with Acmez
Share what you need to change, build, integrate or support. We will map the practical next step.