API testing involves multiple rounds of API executions using both valid and invalid data. Traditionally, this is done manually by a tester. It can be performed using tools like a cURL command prompt or other API testing tools.

In API test automation, the same process is executed using a tool or script. To provide visibility into the testing, the inputs and outputs are captured and presented as reports. API test automation is designed and configured manually once, and then executed multiple times. This becomes especially useful when the objective is in-depth testing or regression testing.

With API test automation, teams can reduce repetitive effort and catch defects early. It also enables testing teams to support frequent releases and continuous integration workflows.

When is API test automation data-driven?

To test a single API endpoint, there are multiple scenarios involving both valid and invalid data, such as:

• Changing the HTTP method
• Changing the URL
• Changing header values
• Changing body attribute values

When different combinations of these inputs are tried, the number of scenarios increases rapidly. The setup where a single API endpoint is tested across many data variations in a systematic way is called data-driven testing. With tools or scripts, managing a large number of scenarios becomes easier. The more scenarios covered, the higher the testing coverage.

When using tools or scripts, the objective should be to keep the test logic fixed while varying the input data. This is achieved by connecting external data sources to the test logic. A data source can be a CSV file, a database, or a JSON file. To increase test coverage, the team simply needs to add more data to these files or databases.

Special case of data-driven testing: Authentication credentials

Since most APIs require authentication before processing requests, authentication handling is an important part of API automation. Tools usually provide in-built capabilities where users configure authentication credentials once, and these credentials are automatically applied to every request.

Extra care is needed when authentication is time-sensitive, such as bearer tokens. In such cases, the tool should be instructed to fetch a fresh token when the existing one expires.

What output is expected from API test automation?

The results of API test automation should closely match the results obtained from manual API testing, but across a much larger number of requests. The output should clearly indicate which API endpoints were tested, what data was used, and what responses were received.

Going a step further, API test automation can also add result indicators such as Passed or Failed, along with the reason for failure. This helps teams quickly identify failing scenarios and investigate them manually in detail. This capability of verifying API responses is called an assertion. The most common assertion is checking the API response status code, such as 200, 401, or 204.

In BusStop, a no-code API testing tool, there are two types of in-built assertions applied to every API response:

• Status check – By default, BusStop checks whether the API response status is 200.
• Schema check – BusStop compares the API response structure and attribute values against the expected response.

Read more here: BusStop in-built assertions

Why API test automation matters

API test automation improves both testing speed and release quality. It validates API behaviour and highlights defects early. Since it is automated, teams can rely on it to handle repetitive testing tasks consistently, release after release.