API testing services
API testing services for REST, GraphQL, gRPC and event-driven systems: functional and regression tests in Postman, REST Assured and code, contract testing with Pact, OpenAPI schema validation, integration tests with mocked third parties, and API security and load checks, with dedicated API test engineers for your team or API testing projects delivered end to end.
API testing we do
Functional API testing
Every endpoint checked for status codes, response bodies, headers, validation errors, pagination and the permissions of each role, explored in Postman, Bruno or Insomnia while the API is new.
Postman collections in the pipeline
Collections organised by feature, with environments, pre-request scripts and assertions, run on every build with the Postman CLI and the results published beside the build.
API test suites in code
REST Assured or Karate for Java teams, pytest with HTTPX for Python, xUnit with HttpClient for .NET and Playwright’s request API or SuperTest for TypeScript, kept beside the service code and reviewed with it.
Contract testing with Pact
Consumer-driven contracts in Pact between web front ends, mobile apps and services, verified in the provider’s build and shared through a Pact Broker or PactFlow, so a breaking change fails the build of the team that made it.
OpenAPI and schema validation
Responses validated against the OpenAPI or JSON Schema definition, specifications linted with Spectral, and Schemathesis generating requests from the specification to find the inputs that cause a server error.
Integration tests with real dependencies
Services started with their database, cache and message broker in Testcontainers, data seeded for each test, and the whole flow checked through the API instead of against a mocked database.
Mocks and service virtualisation
Third-party and unfinished services replaced with WireMock, Mock Service Worker or Microcks, so tests run without a partner’s sandbox and cover the timeouts, rate limits and error responses that are hard to trigger for real.
GraphQL, gRPC and message testing
GraphQL queries, mutations and field-level authorisation, gRPC services called through grpcurl and generated clients, and Kafka, RabbitMQ or Azure Service Bus messages checked for schema, ordering and duplicates.
API security and load checks
Authentication, object-level authorisation, input validation and rate limits checked against the OWASP API Security Top 10 in every regression run, and response times under load measured with k6 before a release.
Hire API test engineers
Dedicated API test engineers
API test engineers who join your team full time, work in your tools and process, and report to your lead. You interview them; we carry the Ukrainian contract, payroll, invoicing and leave.
API testing projects
A defined piece of API testing with a scope, a fixed plan and a named lead on our side who owns the result and reports progress in your channels.
Ongoing API testing
API testing as a continuing service: the same people every month, a backlog you prioritise, and hours you can see in our portal and on the invoice.
The dedicated team page explains how specialists join your team, and the outsourcing page covers project delivery, take-overs and how we charge.
Who works on your API testing
API test engineers
Collections, coded suites and contract tests
Backend developers
Testable APIs, provider verification and fixes
Test automation engineers
Frameworks and CI integration
Performance engineers
Load tests on the busiest endpoints
How we test APIs
API tests carry most of the regression load because they are fast and stable: hundreds of checks finish in minutes on every pull request, and the browser suite is left with the journeys that need a screen. Tests are written from the specification and the business rules, so they catch a field that changed meaning as well as one that disappeared.
Each test creates its own data through the API and removes it afterwards, so runs never depend on each other or on a shared database someone edited by hand. Credentials for test environments come from the pipeline’s secret store, never from a collection file committed to the repository.
Other software testing services
Manual testing
Manual testing services: functional, regression and exploratory testing, test case design, cross-browser and cross-device testing and UAT support, with dedicated manual QA engineers or project delivery.
Test automation
Test automation services: Playwright, Selenium, Cypress and WebdriverIO suites, SDET work, API and visual tests, and CI integration, with dedicated test automation engineers or project delivery.
Mobile app testing
Mobile app testing services: iOS and Android testing on real devices and device farms, Appium, Espresso, XCUITest and Maestro automation, and store release checks, with dedicated mobile QA engineers or project delivery.
Performance testing
Performance and load testing services: load, stress and soak tests in k6, JMeter, Gatling and Locust, bottleneck analysis, capacity planning and Core Web Vitals, with dedicated performance engineers or project delivery.
Accessibility testing
Accessibility testing services: WCAG 2.2 audits, screen reader and keyboard testing, axe checks in CI, remediation support and conformance reports, with dedicated accessibility testers or project delivery.
Questions about API testing
Which industries do your API test engineers work in?
Mostly fintech and banking, where payment, ledger and open banking APIs need evidence for every release; e-commerce and marketplaces, with catalogue, order and partner integrations; enterprise SaaS and ERP products with public APIs and many integrations; healthcare, with HL7 FHIR interfaces between clinical systems; and telecom, cloud and logistics platforms built from many services.
Postman or tests in code?
Both have a place. Postman is quick for exploring a new API and sharing working requests with the team. As the API settles, the checks move into code in the service’s own language, where they are reviewed in pull requests, reuse the service’s models and run with the unit tests.
What does contract testing add?
API tests check that a service behaves as its own team expects. Contract tests check that it still gives each consumer what that consumer actually uses, so a renamed field or a changed type fails the provider’s build before it breaks a mobile app or another team’s service in production.
How quickly can API test engineers start?
When the right API test engineer is available, the start is gated only by your interview and the NDA and IP assignment. Otherwise we run a search, which typically produces candidate profiles within two to three weeks, and nobody starts until you have said yes.
How do we hire API test engineers through BigTree108?
Tell us the work, the seniority and the hours you need. We propose one or two people with their profiles, you interview them the way you would interview your own hire, and you sign one agreement with BIG TREE 108 LLC and receive one invoice a month.
Who owns the work they produce?
You do. Every specialist has a signed contract with BigTree108 that assigns all work product to the company, and our agreement with you assigns it onward. Code, designs and documents are delivered into your own repositories and tools, not kept where only we can change them.
Need your APIs tested?
Tell us how many services you run, how their APIs are documented and who calls them. You get an answer within one business day: a test plan, candidate profiles, or a scope for a review of your API tests.