Why pre-request scripts prepare data in Postman - Test Execution Impact

Test Overview

This test checks that a Postman pre-request script correctly prepares data before sending an API request. It verifies that the data is set in the environment and used in the request body.

Test Code - Postman Sandbox

Postman

pm.test("Pre-request script sets data correctly", () => {
    // Run the pre-request script manually
    pm.environment.set('userId', '12345');

    // Simulate sending a request using the prepared data
    const requestBody = {
        id: pm.environment.get('userId'),
        name: 'Test User'
    };

    // Assert the userId is set correctly
    pm.expect(pm.environment.get('userId')).to.eql('12345');

    // Assert the request body uses the prepared data
    pm.expect(requestBody.id).to.eql('12345');
});

Execution Trace - 4 Steps

Step	Action	System State	Assertion	Result
1	Test starts	Postman environment is clean with no userId set	-	PASS
2	Pre-request script sets environment variable 'userId' to '12345'	Environment variable 'userId' is now '12345'	Check environment variable 'userId' equals '12345'	PASS
3	Prepare request body using environment variable 'userId'	Request body contains { id: '12345', name: 'Test User' }	Verify requestBody.id equals '12345'	PASS
4	Assertions verify environment variable and request body data	Assertions pass confirming data preparation	pm.expect(pm.environment.get('userId')).to.eql('12345') and pm.expect(requestBody.id).to.eql('12345')	PASS

Failure Scenario

Failing Condition: Pre-request script fails to set environment variable 'userId'

Execution Trace Quiz - 3 Questions

What does the pre-request script do in this test?

A Sets environment data needed for the request

B Sends the API request

C Checks the response status

D Clears environment variables

Key Result

Always use pre-request scripts to prepare and set data needed for your API requests to ensure tests run with correct inputs.