Day 13 of 60
·
Unit, integration, contract
Contract testing
In a microservice architecture, "we agreed on the API last sprint" is a fairy tale. Contracts make the agreement machine-checkable, both sides, every PR.
ProblemService A and Service B agree on a contract; either side breaks it without warning.
How it works
Each side declares its expectations as a machine-checkable contract. Pre-merge, both sides verify the contract. Failures block deploy.
What it catches
Cross-service breakages, especially in microservice architectures. Catches what end-to-end tests catch but with 1/10th the runtime.
Tools
Pact · OSS Spring Cloud Contract · OSS JSON Schema · OSS
Verdict by project size
Small
Skip
Medium
Rec
Large
Must
Extra-large
Must
Cost
| Project size | Setup | Maint / mo | Tool / mo | CI / run |
|---|---|---|---|---|
| Small <10k LOC | 1d | 1h | $0 | +1m |
| Medium 10–100k LOC | 3d | 5h | $0 | +2m |
| Large 100k–1M LOC | 10d | 25h | $500 | +5m |
| Extra-large >1M LOC | 30d | 80h | $2k | +10m |
Setup = engineer-days to first useful run ·
Maint = engineer-hours / month at steady state ·
Tool = out-of-pocket $ / month ·
CI = minutes added (or saved) per pipeline run
Lifecycle & ownership
When in lifecycle
Code Test
Per pull request · Runs in CI on every PR; gates merge.
Who owns it
Developer
Authoring + the inner loop
Collaborates with: QA / Test Engineer
Reference implementations
-
Pact JS examples
Consumer-driven contract testing examples for HTTP and asynchronous interfaces.
-
Pact JVM examples
Provider and consumer contract test patterns across JVM stacks.
-
Spring Cloud Contract samples
Contract-first service validation using generated tests and stubs.
Quick check
In a microservice architecture, contract testing replaces what?
One question. Pick the best answer. Your streak is saved locally on this device.
Save the lesson
Download SVG ↓
Screenshot for a 1:1, drop it in Slack, or download the SVG.