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Data-driven testing in Postman

Data-driven testing (DDT) is an automated testing strategy used to run a suite of tests where the test input and output values are driven by data input. In software testing, DDT allows testers to validate  application functionality under different input scenarios effectively. Postman offers these capabilities for implementing data-driven tests. This article shows how to set up and executing data-driven tests in Postman, using its features to maximize test coverage.

Understanding Data-Driven Testing

Data-driven testing involves executing a series of tests repeatedly using input values provided from an external data source. This approach helps in:

  • Reducing the number of test scripts needed, as the same test can be run with different data.
  • Identifying edge cases and enhancing test coverage.
  • Ensuring the usefulness of the application by testing different combinations of data inputs.
  • Improving API development by validating requests with diverse datasets.

Setting Up Postman for Data-Driven Testing

Postman utilizes collections, environments, and data files to facilitate DDT. Here’s how you can set up your environment for data-driven testing:

1. Preparing Data Files

Postman supports data files in JSON and CSV formats. These files should be structured to match the variables in your API requests. For example, if your API requires a username and password, your data file could look like this in JSON:

[

  {“username”: “user1”, “password”: “pass1”},

  {“username”: “user2”, “password”: “pass2”}

]

And like this in CSV:

username,password

user1,pass1

user2,pass2

2. Creating API Requests

In Postman, you create a new collection and add API requests. Variable names in the request URL, headers, or body can be specified using double curly braces, e.g., {{username}} and {{password}}.

3. Using the Collection Runner

The Collection Runner is a powerful feature in Postman that lets you run a series of API calls. To perform data-driven testing:

  • Open the Collection Runner.
  • Select the collection you want to test.
  • Attach the data file under the Data file option.
  • Click on Run.

Postman will execute the collection of API requests, substituting the variables with values from each row in your data file.

Advanced Features for Data-Driven Testing

  1. Using Postman Scripts

You can enhance DDT in Postman using the Pre-request Script and Tests tabs. These allow you to execute JavaScript before a request is sent and after a response is received, respectively. For example, you can use scripts to:

  • Validate the response data against expected output in your data file.
  • Manipulate data before sending it in a request.
  1. Dynamic Data Generation

Sometimes, static data files may not be sufficient, especially when you need unique data for each test run (like timestamps or unique identifiers). Postman’s Pre-request Script can generate dynamic data:

pm.variables.set(“timestamp”, new Date().getTime());

  1. Integrating with Continuous Integration Systems

Data-driven tests can be integrated into CI/CD pipelines using Postman’s command-line tool, Newman. Newman allows you to run collections directly from the command line. It is used for automating tests as part of build processes.

newman run Collection.postman_collection.json -d datafile.json

Best Practices for Data-Driven Testing in Postman

  • Keep your data files organized and easy to understand. This makes it easier to modify tests or add new data scenarios.
  • Regularly update your tests and data. As your application evolves, so should your tests and the data they use.
  • Use meaningful test data. Ensure the data used is representative of real-world scenarios to catch more bugs.
  • Review test results thoroughly. Analyze failures to identify any potential issues in the application or the tests themselves.

When to look for a postman alternative?

If you are also looking for a tool to automate your web, mobile and desktop application tests along with API tests, then postman might not be the right tool for you.

A tool like Testsigma could be the right alternative here:

Testsigma is a low-code test automation platform that lets you automate your tests for web, mobile, desktop as well as APIs, from the same place. Here, you automate your tests in simple English and can customize them with JAVA. This tool also is completely cloud-based so you can start automating and executing your tests in minutes. You may signup here: Testsigma free trial 

Conclusion

Data-driven testing in Postman is a powerful approach to enhance the quality and reliability of API services. By leveraging Postman’s capabilities for DDT, you can efficiently validate API behaviors under various conditions and integrate these tests into broader automation frameworks, ensuring robust and reliable API performance.

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