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API & Integration Testing

Most integration failures don't show up on a screen. A payment callback arrives twice, an error returns 200 with an empty body, a token works after it should have expired. We test the API layer directly, so those problems are found before your apps and partners depend on them.

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Problems this finds

  • Responses that don't match the documented contract: missing fields, wrong types, inconsistent status codes
  • Validation gaps: accepted values that should be rejected, unclear or leaky error messages
  • Access rules: endpoints reachable without the right token, role or ownership
  • Integration hand-offs: duplicated, out-of-order or lost webhooks and callbacks, and how retries behave
  • Data that the API reports as saved but that is stored incompletely or differently

In scope

  • REST and JSON APIs, using your specification (for example OpenAPI) or agreed examples
  • Positive and negative cases, boundary values and authentication rules
  • Webhooks and callbacks to and from payment, messaging and partner services, in a test environment
  • Checking stored results with read-only SQL where access is provided

Not included

  • Load and stress testing — see Performance Testing
  • Penetration testing or a formal security audit
  • Testing against production payment or partner accounts

How we work

We test your APIs directly — contracts, error handling, authentication rules — and the hand-offs between systems such as payment, messaging, and third-party services, so problems are found before they reach your apps and partners.

  1. 1Review specifications and integrations
  2. 2Design positive and negative cases
  3. 3Execute and record evidence
  4. 4Report and retest fixes

What you receive

  • Endpoint coverage mapped against your API specification
  • Reproducible defect reports with request and response evidence
  • Findings on validation, error handling, access rules, and integration hand-offs
  • Reusable request collections your team can keep using

What this looks like in practice

Our free tools show the kind of evidence we work with. API Workspace sends requests from your browser and shows status, timing, headers and body. Webhook Inspector gives you a temporary inbox to see exactly what a payment or messaging provider sends. The Payment Journeys training mission covers repeated submissions and payment states on a purpose-built app.

Related Learn QA lessons

Free lessons from our QA Lab that explain the same ideas in more depth.

Testing reduces risk and improves confidence — no testing approach can guarantee defect-free software, and we will never claim otherwise.