REST API testing: key checks and CI/CD integration
A REST API is an interface through which systems exchange data using HTTP requests. In a test, we call its endpoints and check the response without going through the user interface. This article focuses on rules specific to REST and on turning those checks into a maintainable test suite.
What is the problem?
Many teams test primarily through application screens because they are closest to what the customer sees. Many application rules can, however, be checked directly through the API more quickly and with more precise information about the cause of a defect.
REST also makes it easy to overlook things that are not visible through the UI at all: whether an endpoint follows the semantics of HTTP methods, returns the correct status code and can be retried safely. This is where defects arise that break a partner integration even though everything looks correct in the browser.
What is specific to REST?
In addition to standard API checks, we verify matters that follow directly from how REST is intended to work:
- The meaning of HTTP methods—that
GETdoes not change data, a repeatedPUTorDELETEhas the expected result, andPOST,PUTandPATCHare used consistently with the API design. - Status codes—that the correct code is returned (
200,201,204,400,401,403,404,409…), rather than “always 200 with an error hidden in the body”. - Safe request retries—for example, that a client retry after a network failure does not create a second payment or order. For
POSToperations, this is often handled using a unique request key known as an idempotency key. - Pagination, filtering and sorting—that a large list is returned in pages and the parameters actually work.
- Versioning and backwards compatibility—that an API change does not break existing clients; contract tests build on this need.
- Headers and format—the correct
Content-Typeand the handling of a missing or invalid header.
Which tools we use and how
Tests can be written in Python with pytest, in Bruno or in Playwright. The choice depends on the team’s technology and experience. We store test files in Git so that their change history is visible alongside application changes.
CI/CD can run quick checks for every change and a broader suite, for example, before a release. The team decides which failures should stop deployment according to risk. If you have an up-to-date OpenAPI specification, we use it to check the interface format and design some of the inputs.
What you gain
- Generally faster feedback than from the same checks performed through a browser.
- Defects in status codes, request retries or pagination detected directly at the REST layer.
- A more precise test result that helps the team locate the cause more quickly.
Next step
Start with a list of critical endpoints, clients and defects that would have the greatest impact. If you would like to review the proposed coverage with us, use a no-obligation consultation.