Regression testing plays a vital role in maintaining the overall quality and performance of your API. Regression tests ensure that your API keeps working as expected after any updates or changes. They can also identify new bugs or issues introduced during development and verify that your changes are backwards compatible.

About regression testing

When making updates or enhancements to an application, it’s important to confirm that those changes don’t have a negative impact on any existing functionality. Regression testing involves running a series of tests to make sure the changed components work alongside the rest of the application and don’t introduce any new defects. These kinds of defects are often calledregressions.

For an API, regression testing means verifying that updates made to the API or its environment don’t affect any other components that depend on it. Regression tests can be run after any sort of change, such as fixing a bug or adding a new feature. The tests can cover the following types of API elements:

• Status code - Verify the API returns the expected status codes for different types of requests.
• JSON schema - Verify the structure and format of a response matches the API definition.
• Response time - Verify the API’s response time is within acceptable limits.
• Response body - Verify the structure and content of the response body matches expectations.
• Headers - Verify the response headers are present and correct.

You can use automation tools like the Postman CLI to run regression tests before releasing code updates and make sure breaking changes don’t make it into production. You can also schedule tests using theCollection Runner to monitor test results over time and get insights into the reliability of your API.

View an example that shows how you can use Postman to set up and run regression tests for your API using Postman’sRegression testing template collection.

Regression test setup in Postman

To set up regression tests for your application in Postman, use the following framework:

• The basic unit of testing is an API request. Each request tests a specific piece of functionality by calling an API endpoint. You can configure request authorization as needed. You can also send any required test data such as parameters, headers, and body data. Learn more aboutcreating and sending requests.

• Write scripts to add test logic to requests. For each request, you can write test scripts to check if the expected data is received when the request is sent. You can test and validate the response code, headers, body data, and more. Learn more aboutwriting test scripts.

• Organize suites of tests using collections. You can save multiple requests in a collection and organize them into categories. Collections enable you to run and rerun a group of tests in the order you choose. You can also upload data files to run tests multiple times using different data each time. Learn more aboutcreating collections.

  You can also add a test suite to an API in Postman. Learn more atAdd automated tests and CI integrations in the Postman API Builder.

• Use scripts to build complex workflows. With scripts, you can process response data from one request and use it as an input in the next request to test data flow. You can also use scripts to dynamically control the order of requests. For example, send a request to create a user account, then send another request to get the new account and verify that it was created. Learn more aboutprocessing data and building workflows with scripts.

• Run your tests in multiple environments. In Postman, environments are groups of related variables you can use in your requests. Environments enable you to reuse the same suite of tests in different contexts. For example, if your test and production setups require different URLs or configuration values, you can use Postman environments to switch between them. Learn more aboutworking with environments and variables.

• Simulate other systems with mock servers. You can test how your application interacts with other APIs and systems without having to connect to the actual resources. Instead, you can use Postman to set up a mock server that simulates the behavior of a real API server by accepting requests and returning responses. Learn more aboutsetting up mock servers.

Run regression tests in Postman

After setting up your regression tests in Postman, you can run them in the following ways:

• Run tests manually. To run a single test, open a request and send it. You can view the test results in the workbench. To run an entire test suite, use theCollection Runner. As the collection runs, Postman displays the test results in real time. Learn more aboutrunning tests manually in Postman.

• Automate tests on a schedule. You can run test suites automatically on a schedule using theCollection Runner. Get notifications when tests fail, and view test results in Postman. Learn more aboutrunning API tests on a schedule in Postman.

• Run tests in your CI/CD pipeline. You can run tests as part of your regular application build process using the Postman CLI. Run your test suites after every code push and view test reports in Postman. Learn more aboutrunning API tests in your CI/CD pipeline.