Quality Engineering
Integration TestingThe bugs live between the modules. We test there.
Most production incidents aren't inside a module, they're between modules: mismatched contracts, silent failures, retry storms. We test the seams: service-to-service interfaces, data flows, and third-party integrations.
What this covers
Service-to-service interface and contract Testing
Data-flow validation across module boundaries
Third-party API integration Testing with failure-mode coverage
Message-queue and event-driven flow validation
Stub/mock strategy for isolating each seam
Defects live in the seams
Components that pass their own tests routinely fail when connected.
Components that pass their own tests routinely fail when connected. One service sends a string where another expects a number. A retry policy turns one payment into three. A queue delivers messages twice, or out of order, and the consumer was written assuming neither could happen. An identity provider returns a slightly different claim shape after an upgrade. Every one of these is invisible to component-level Testing and obvious in production.
Integration Testing targets those boundaries deliberately: service to service, service to database, service to queue, and application to third party. It is the cheapest place to catch the most expensive category of defect, because a contract violation found in a pipeline costs an hour and the same violation found in production costs an incident.
The failure modes we test for
Where teams deploy independently, consumer-driven contract Testing is the highest-leverage control available, it moves the failure into the provider's pipeline at the moment they introduce it.
Where teams deploy independently, consumer-driven contract Testing is the highest-leverage control available, it moves the failure into the provider's pipeline at the moment they introduce it. The practical pattern is in Shift-Left API Contract Testing, and the tooling side sits with our API Testing practice.
Contract mismatches: field types, optionality, enum drift, date formats, and the version skew that appears when two services deploy independently.
Asynchronous behaviour: duplicate delivery, out-of-order messages, poison messages, retry storms, and whether consumers are genuinely idempotent.
Third-party failure: timeouts, partial outages, rate limits and malformed responses from payment, identity, messaging and analytics providers.
Transaction boundaries: what happens when step three of a five-step distributed workflow fails, and whether compensation actually restores a consistent state.
Authentication across boundaries: token propagation, expiry mid-workflow, and permission enforcement at every hop rather than only the first.
Testing what you do not control
You cannot ask a payment provider to be slow on demand, so we build the ability to simulate it: mocks and stubs that reproduce timeouts, rate limits, error payloads and malformed responses on request.
You cannot ask a payment provider to be slow on demand, so we build the ability to simulate it: mocks and stubs that reproduce timeouts, rate limits, error payloads and malformed responses on request. That gives repeatable coverage of failure paths that would otherwise be tested for the first time during an outage, and it removes the third party as a source of flake in your pipeline.
Engagement path
How the engagement runs
Every Integration Testing engagement runs the same way: understand the risk, build the thing that reduces it, prove it works, hand it over.
Boundary inventory
We map every integration point, services, queues, databases, third parties, and rank them by how badly a silent failure would hurt.
Contracts and schema gates
Schema validation and consumer-driven contracts wired into CI so incompatible changes fail the provider's build, not a downstream environment.
Failure simulation
Mocks and stubs that reproduce timeouts, rate limits, duplicate deliveries and malformed responses, making failure paths repeatable and testable.
End-to-end verification
Distributed workflows validated across all hops, including compensation logic when a middle step fails.
Deliverables
What you get
Artefacts you keep and can run without us. Everything lives in your repositories and your tooling.
Handover pack
6 artefacts · yours to keep
A documented inventory of every integration boundary and its failure impact
Consumer-driven contract tests running in the correct pipelines
A mock and stub layer reproducing third-party failure on demand
Idempotency, ordering and duplicate-delivery coverage for async flows
Distributed transaction and compensation-path results
CI reporting that names the contract and the commit that broke it
Self-check
Signs your team needs this
If more than one of these is true, it is usually cheaper to fix now than after the next release.
A backend change broke a consumer and nobody found out until release
Third-party outages produce unpredictable behaviour you cannot reproduce
Retries have caused duplicate charges, emails or records at least once
Services deploy independently with no contract enforcement between them
Failure paths across services have never been deliberately exercised
A Senior Engineer replies within one business day. NDA first.
Questions
Frequently Asked Questions
Straight answers, written the way we'd say them on a call.
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Where to go next
Integration Testing rarely stands alone. These are the disciplines and resources teams pair it with most often.
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