For this contract testing example, I used JSONPlaceholder to validate that required fields exist and follow the expected data types, ensuring a consistent API contract and preventing breaking changes.
Step to Reproduce:
- Create a GET request in Postman using
https://jsonplaceholder.typicode.com/posts/1 - Send the request and capture the JSON response
- Add tests to validate required fields and data types.
- Verify that the response structure remains consistent across executions.
API Contract Testing Workflow:

Testing Execution in Postman:
- Send GET request to
/posts/1 - Validate fields such as
userId,id,title, andbody - Check that each field matches the expected data type
- Confirm that the response contract is stable.

What This Demonstrates:
- API contract validation
- Response structure consistency
- Required field and type verification
- Detection of breaking changes between API consumers and backend.
“Consistency in structure is what keeps systems connected.”