Run Postman collection with data file using Newman

Preconditions (3)

Step 1: Open terminal or command prompt

Step 2: Run Newman command with the collection file and data file using --iteration-data option

Step 3: Wait for Newman to execute all iterations

Step 4: Observe the test run results for each data set

✅ Expected Result: Newman runs the collection once for each data set in the data file and shows pass/fail results for each iteration

Automation Requirements - Newman CLI

Assertions Needed:

Verify Newman runs all iterations equal to the number of data rows

Verify each iteration passes all tests in the collection

Best Practices:

Use --iteration-data option to specify data file

Use JSON or CSV format for data file

Check exit code of Newman command for success

Use descriptive names for data sets in the file

Automated Solution

Postman

const { exec } = require('child_process');

const collectionFile = 'path/to/collection.json';
const dataFile = 'path/to/data.json';

exec(`newman run ${collectionFile} --iteration-data ${dataFile} --reporters cli,json --reporter-json-export newman-report.json`, (error, stdout, stderr) => {
  if (error) {
    console.error(`Error executing Newman: ${error.message}`);
    process.exit(1);
  }
  if (stderr) {
    console.error(`Newman stderr: ${stderr}`);
  }
  console.log(`Newman output:\n${stdout}`);

  // Simple check for iterations run
  const iterationsMatch = stdout.match(/iterations:\s*(\d+)/i);
  if (iterationsMatch) {
    const iterations = parseInt(iterationsMatch[1], 10);
    console.log(`Iterations run: ${iterations}`);
  } else {
    console.warn('Could not find iterations count in output');
  }

  // Check for failures
  const failuresMatch = stdout.match(/failed:\s*(\d+)/i);
  if (failuresMatch) {
    const failures = parseInt(failuresMatch[1], 10);
    if (failures === 0) {
      console.log('All tests passed for all iterations.');
    } else {
      console.error(`There are ${failures} test failures.`);
      process.exit(1);
    }
  } else {
    console.warn('Could not find failures count in output');
  }
});

This Node.js script runs Newman CLI using child_process.exec to execute the Postman collection with the data file.

The --iteration-data option tells Newman to run the collection once per data row.

The script captures the output and parses it to find how many iterations ran and how many tests failed.

If there are any failures, the script exits with error code 1 to indicate test failure.

This approach automates running the collection with multiple data inputs and verifies the results programmatically.

Common Mistakes - 4 Pitfalls

Not using --iteration-data option and running collection only once

Using incorrect path or filename for collection or data file

Ignoring Newman exit code and output

Using data file with wrong format or invalid JSON/CSV

Bonus Challenge

Now add data-driven testing with 3 different input data sets in the data file and verify all iterations pass

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