Looping in flows in Postman - Build an Automation Script

Automate looping through multiple API requests in Postman collection runner

Preconditions (3)

Step 1: Open the Postman collection runner

Step 2: Select the collection containing the API request

Step 3: Load a data file (CSV or JSON) with multiple sets of input data

Step 4: Start the collection runner to execute the request for each data row

Step 5: Observe that the request runs once per data row, looping through all inputs

Step 6: Verify the response status code is 200 for each request

Step 7: Verify the response body contains expected data for each input

✅ Expected Result: The collection runner executes the API request once per data row, looping through all inputs. Each response returns status 200 and expected data.

Automation Requirements - Postman test scripts with Collection Runner

Assertions Needed:

Verify response status code is 200

Verify response body contains expected data based on input

Verify the loop runs for all data rows

Best Practices:

Use pm.test() for assertions

Use data-driven testing with external data files

Use pm.iterationData to access current data row

Keep test scripts simple and readable

Automated Solution

Postman

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

const expectedValue = pm.iterationData.get('expectedValue');

pm.test('Response body contains expected value', () => {
    const jsonData = pm.response.json();
    pm.expect(jsonData.value).to.eql(expectedValue);
});

This Postman test script runs after each API request in the collection runner.

First, it checks that the response status code is 200 using pm.response.to.have.status(200).

Then, it retrieves the expected value for the current iteration from the data file using pm.iterationData.get('expectedValue').

Finally, it asserts that the response JSON's value field equals the expected value.

This script runs once per data row, enabling looping through inputs in the collection runner.

Common Mistakes - 3 Pitfalls

Hardcoding expected values inside the test script instead of using data files

Not checking the response status code before validating response body

Using console.log for validation instead of pm.test assertions

Bonus Challenge

Now add data-driven testing with 3 different inputs using a JSON data file

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