Data file integration (CSV, JSON) in Postman - Build an Automation Script

Run API tests using data file integration with CSV and JSON in Postman

Preconditions (3)

Step 1: Open Postman and create a new collection

Step 2: Add a new request to the collection with the API endpoint

Step 3: Set the HTTP method and required headers

Step 4: Click on the Runner button to open the Collection Runner

Step 5: Select the collection containing the request

Step 6: Click on 'Select File' and upload the CSV data file

Step 7: Start the run and observe the results

Step 8: Repeat the run using the JSON data file instead of CSV

Step 9: Verify that each request uses data from the file and responses are as expected

✅ Expected Result: The API requests run multiple times using each row/object from the CSV and JSON files. Each response matches the expected output for the input data.

Automation Requirements - Postman Collection Runner

Assertions Needed:

Verify response status code is 200 for each request

Verify response body contains expected data matching input

Verify all data rows/objects from the file are used

Best Practices:

Use variable placeholders in the request URL, headers, or body to inject data

Use pre-request scripts or tests to validate data-driven execution

Keep data files clean and well-structured

Use descriptive names for variables and data columns/keys

Automated Solution

Postman

/* Postman test script example for data-driven test using CSV or JSON */

// In the request body or URL, use variables like {{username}}, {{password}}

// Example test script to verify response
pm.test('Status code is 200', () => {
    pm.response.to.have.status(200);
});

pm.test('Response contains username', () => {
    const jsonData = pm.response.json();
    pm.expect(jsonData.username).to.eql(pm.iterationData.get('username'));
});

// No additional code needed to load data files; handled by Collection Runner

// To run:
// 1. Open Collection Runner
// 2. Select collection
// 3. Select CSV or JSON file with columns/keys like username, password
// 4. Run and observe test results for each data row/object

// Example CSV file content:
// username,password
// user1,pass1
// user2,pass2

// Example JSON file content:
// [
//   {"username": "user1", "password": "pass1"},
//   {"username": "user2", "password": "pass2"}
// ]

This Postman test script uses variable placeholders like {{username}} and {{password}} in the request to inject data from the CSV or JSON file during the Collection Runner execution.

The test script verifies that the response status code is 200 and that the response body contains the expected username matching the input data for each iteration.

The Collection Runner automatically reads the data file and runs the request once per data row (CSV) or object (JSON), replacing variables accordingly.

This approach keeps the test simple and reusable for any data file with matching keys.

Common Mistakes - 4 Pitfalls

Not using variable placeholders in the request to inject data

Uploading data file with incorrect format or missing headers/keys

{'mistake': 'Not verifying response data against input data', 'why_bad': 'Tests may pass without confirming the API processed the input correctly, missing bugs.', 'correct_approach': "Write assertions comparing response fields to input data using pm.iterationData.get('variableName')."}

Running tests without using Collection Runner

Bonus Challenge

Now add data-driven testing with 3 different inputs using both CSV and JSON files

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