Data-driven testing is a powerful technique that allows you to run the same test with multiple sets of data. This approach is particularly useful for testing APIs with various input values to ensure they handle different scenarios correctly. In this section, we'll explore how to perform data-driven testing using Postman.

1. Data-Driven Testing: A testing methodology where test data is stored in an external file (like CSV or JSON), and the same test is executed multiple times with different data sets.

2. Postman Collection Runner: A feature in Postman that allows you to run collections with different data sets.

3. Data Files: External files (CSV or JSON) that contain the data sets used for testing.

• CSV File: A simple text file where each line represents a data set, and each value is separated by a comma.

  Example CSV:

  username,password
  user1,pass1
  user2,pass2
  user3,pass3
  

• JSON File: A structured file where data is organized in key-value pairs.

  Example JSON:

  [
    {"username": "user1", "password": "pass1"},
    {"username": "user2", "password": "pass2"},
    {"username": "user3", "password": "pass3"}
  ]
  

• Collection: A group of requests that can be run together. Create a new collection in Postman and add the request you want to test.

• Replace static values in your request with variables that will be populated with data from your data file.

  Example Request Body:

  {
    "username": "{{username}}",
    "password": "{{password}}"
  }
  

• Open the Collection Runner in Postman.
• Select the collection you want to run.
• Choose the data file (CSV or JSON) you prepared.
• Click "Run" to execute the tests with each data set.

• Postman will display the results for each iteration, allowing you to see which data sets passed or failed.

Let's create a simple test to authenticate users with different credentials.

1. Create a New Request:

   • Method: POST
   • URL: https://api.example.com/auth/login
   • Body (raw, JSON):

     {
       "username": "{{username}}",
       "password": "{{password}}"
     }
     

2. Add the Request to a Collection:

   • Create a new collection named "User Authentication".
   • Add the request to this collection.

3. Prepare the Data File:

   • Save the following CSV content as users.csv:

     username,password
     user1,pass1
     user2,pass2
     user3,pass3
     

4. Run the Collection:

   • Open the Collection Runner.
   • Select "User Authentication" collection.
   • Choose users.csv as the data file.
   • Click "Run".

5. Review the Results:

   • Check the results for each user to ensure the API handles each set of credentials correctly.

• File Format: Ensure your data file is correctly formatted. CSV files should not have extra commas, and JSON files must be valid JSON.
• Variable Names: Make sure the variable names in your request match the headers in your data file.
• Data File Path: When selecting the data file, ensure the path is correct and the file is accessible.

Data-driven testing in Postman allows you to efficiently test your APIs with multiple data sets, ensuring robustness and reliability. By following the steps outlined above, you can automate and streamline your testing process, making it easier to identify issues and improve your API's performance. In the next section, we'll explore how to test RESTful APIs using Postman, building on the skills you've learned here.