Like any software, APIs are subject to bugs and other errors. That makes API testing at least as important as other software testing, likely more-so. With potentially hundreds or thousands of consumers, an issue in your API could have a magnifying effect. To maintain software quality, it makes sense to have a robust approach to API testing.
Types of API Testing
You may interpret API testing in several ways. In most cases, you’ll likely want to perform multiple types of tests. These happen at different stages of the API lifecycle and are likely performed by different people within your company.
While not inclusive, here are some of the common ways to test APIs:
- Unit testing: Like other software built with test-driven development, you can test your actual API methods for expected results.
- Integration testing: After the API is built, compare its actual responses to those determined by your “API contract” or definition.
- Security testing: Have experts (internal or external) identify vulnerabilities, or use a proven framework/checklist to confirm security.
- Load testing: Ensure the API is performant by running a load test that simulates actual expected traffic to your API.
You may have other ways you test or other names for the ways you test them. Most important is to approach your APIs with real-world situations, so you’re testing the right things.
Consider How Your API is Used
The ways you test your APIs may differ based on how you expect them to be used. Don’t simply test for testing’s sake. The best way to ensure effective tests is to base them around use cases.
Good API design requires knowing how the API will be consumed. Often, it’s not a single API call. You may need to chain multiple calls together, using data from one response in a subsequent request. Your tests should reflect these real-world scenarios. For integration and load testing, this is especially important, because otherwise you may miss important test cases.
Similarly, look for your API’s dependencies. It may rely on a specific library or another API. Are you able to confirm these dependencies have been tested? You can’t test everything, but at least you can know where to look for potential issues. And the good news is you don’t have to catch everything the first time. You should be revisiting these tests frequently.
Testing Should Happen Continuously
As situations change, your test will, too. Include testing in your API workflow, so your tests remain solid across the lifecycle.
Specifically look out for times when:
- You are making changes to the API
- There is a change in how the API is used
Whenever the API changes or you deploy, run the relevant tests. If you’ve added endpoints or response data, you may need to expand your tests.
When the API doesn’t change, but its usage does, it is a tricky one to catch. You may need a heads up from business development or sales, as often this coincides with a new consumer. If they’re a large company or you’ve agreed to SLAs, running load tests, for example, will help maintain confidence in what you’ve built.
Every type of API testing catches issues while they’re small—perhaps still in development. Your software is built on these interfaces, so proactive testing will help create better products.