3 REST API Testing Mistakes That Cost Us the Most Time (and How We Fixed Them)

Over the last few years, one thing has become obvious to me: writing API tests isn’t the difficult part.

Keeping them useful is.

Across different projects, I kept seeing the same three problems appear repeatedly. None of them were caused by bad tools or poor developers. They were simply the result of APIs evolving faster than the tests around them.

Here are the three changes that made the biggest difference for us.

For a long time we maintained three different versions of the same API:

Someone would update the API but forget to update the tests.

Instead, we started treating the OpenAPI specification as the source of truth.

The API changes once.

Everything else follows.

Even if you aren’t generating tests automatically, having one canonical contract dramatically reduces maintenance.

One mistake we made early was putting every assertion into the same test.

When the test failed, finding the actual cause took time.

Instead we now split responsibilities.

The tests became much easier to understand and much easier to maintain.

For a while we mocked every external dependency.

It was also overconfident.

Eventually we discovered that several production failures were caused by assumptions our mocks never exercised.

Today we use three layers.
• **Pre-release validation – **Run a small suite against real services or official sandbox environments.

It’s slower, but it catches issues that perfect mocks never will.

Authentication tests now consume more CI time than almost anything else.

OAuth flows, token refresh, service accounts, rotating secrets… they’re all necessary, but they’re also expensive to test properly.

I’m curious how other teams are handling this today.
• Doing something completely different?

I’d also be interested to hear how you’re approaching cursor-based pagination and testing third-party APIs e.g. Stripe or Twilio, etc.

Every team seems to have a different answer, and I suspect there isn’t a single “best” solution.…Read more by Rishi Gaurav