Script execution order in Postman - Test Execution Trace

Test Overview

This test checks the order in which Postman scripts run: Pre-request Script runs before the request, and Tests script runs after the response is received. It verifies that variables set in Pre-request Script are available in the request and that Tests script assertions pass.

Test Code - Postman

Postman

pm.environment.set('preRequestVar', 'hello');

// Pre-request Script
// This script runs before the request is sent

// Request URL uses the variable
GET {{baseUrl}}/api/data?greeting={{preRequestVar}}

// Tests Script
pm.test('Response status is 200', function () {
    pm.response.to.have.status(200);
});
pm.test('Response contains greeting', function () {
    const jsonData = pm.response.json();
    pm.expect(jsonData.greeting).to.eql(pm.environment.get('preRequestVar'));
});

Execution Trace - 5 Steps

Step	Action	System State	Assertion	Result
1	Pre-request Script runs and sets environment variable 'preRequestVar' to 'hello'	Environment variable 'preRequestVar' is set to 'hello'	—	PASS
2	Request is sent to URL with variable replaced: GET {{baseUrl}}/api/data?greeting=hello	Request URL is fully resolved with variable value	—	PASS
3	Response is received with JSON containing greeting: 'hello'	Response body: {"greeting": "hello"}	—	PASS
4	Tests script runs: Assert response status is 200	Response status code is 200	pm.response.to.have.status(200)	PASS
5	Tests script runs: Assert response greeting matches environment variable	Response JSON greeting is 'hello', environment variable is 'hello'	pm.expect(jsonData.greeting).to.eql(pm.environment.get('preRequestVar'))	PASS

Failure Scenario

Failing Condition: Pre-request Script does not set the environment variable or variable is not replaced in request URL

Execution Trace Quiz - 3 Questions

Which script runs first in Postman when sending a request?

A Pre-request Script

B Tests Script

C Request Body Script

D Response Script

Key Result

Always use Pre-request Scripts to set or prepare variables before sending requests, ensuring the request uses correct data. Tests scripts should verify the response after the request completes.

Practice

1. In Postman, which script runs first when you send a request?
Collection Pre-request Script, Folder Pre-request Script, or Request Pre-request Script?

easy

A. Collection Pre-request Script

B. Folder Pre-request Script

C. Request Pre-request Script

D. Test Script

Solution

1. Step 1: Understand script types in Postman

   Pre-request scripts run before sending the request. They can be set at collection, folder, or request level.

2. Step 2: Identify execution order of pre-request scripts

   Postman runs pre-request scripts starting from the collection level, then folder, then request level.

3. Final Answer:

   Collection Pre-request Script -> Option A

4. Quick Check:

   Pre-request scripts run top-down: Collection first [OK]

Hint: Pre-request scripts run from collection to request level [OK]

Common Mistakes:

• Thinking request pre-request script runs first
• Confusing test scripts with pre-request scripts
• Assuming folder scripts run before collection scripts

2. Which of the following is the correct syntax to add a test script in Postman that checks if the response status is 200?

easy

A. test('Status is 200', () => response.status === 200);

B. pm.check('Status is 200', () => pm.response.status === 200);

C. pm.assert('Status is 200', pm.response.statusCode == 200);

D. pm.test('Status is 200', function () { pm.response.to.have.status(200); });

Solution

1. Step 1: Recall Postman test script syntax

   Postman uses pm.test() with a callback function to define tests.

2. Step 2: Verify correct assertion method

   pm.response.to.have.status(200) is the correct way to check status code 200.

3. Final Answer:

   pm.test('Status is 200', function () { pm.response.to.have.status(200); }); -> Option D

4. Quick Check:

   Use pm.test() and pm.response.to.have.status() [OK]

Hint: Use pm.test() with pm.response.to.have.status() [OK]

Common Mistakes:

• Using pm.check() which does not exist
• Using test() without pm namespace
• Using pm.assert() which is invalid

3. Given these scripts in Postman:
Collection Pre-request Script: sets variable var1 = 'A'
Folder Pre-request Script: sets var1 = 'B'
Request Pre-request Script: sets var1 = 'C'
After sending the request, what is the value of var1 in the test script?

medium

A. 'C'

B. 'B'

C. Undefined

D. 'A'

Solution

1. Step 1: Understand script execution order for pre-request scripts

   Pre-request scripts run in order: collection, then folder, then request. Each can overwrite variables.

2. Step 2: Trace variable assignment

   Collection sets var1='A', folder overwrites var1='B', request overwrites var1='C'. Final value is 'C'.

3. Final Answer:

   'C' -> Option A

4. Quick Check:

   Last pre-request script sets final variable [OK]

Hint: Last pre-request script overwrites variables [OK]

Common Mistakes:

• Assuming collection script value remains
• Thinking folder script overwrites request script
• Forgetting scripts run before request

4. You wrote a test script in Postman but it never runs after sending the request. Which is the most likely reason?

medium

A. You forgot to save the request

B. The request URL is invalid

C. You placed the script in the Pre-request Script tab instead of Tests tab

D. You did not enable the collection runner

Solution

1. Step 1: Understand when test scripts run

   Test scripts run after the response is received, and must be placed in the Tests tab.

2. Step 2: Identify script placement error

   If the script is in Pre-request Script tab, it runs before sending request, not after response, so test code won't run as expected.

3. Final Answer:

   You placed the script in the Pre-request Script tab instead of Tests tab -> Option C

4. Quick Check:

   Tests run only in Tests tab after response [OK]

Hint: Put test code in Tests tab, not Pre-request tab [OK]

Common Mistakes:

• Confusing pre-request and test script tabs
• Assuming saving request affects script execution
• Thinking collection runner is needed for tests

5. You have a collection with a pre-request script setting a variable token. A folder inside the collection has a pre-request script that updates token only if it is empty. The request inside the folder has a test script that checks if token is set. Which script execution order ensures the test script sees the updated token?

hard

A. Request test script runs before folder pre-request script

B. Collection pre-request script runs first, then folder pre-request script, then request test script

C. Folder pre-request script runs before collection pre-request script

D. Request pre-request script runs after test script

Solution

1. Step 1: Recall Postman script execution order

   Pre-request scripts run in order: collection, folder, request. Test scripts run after response.

2. Step 2: Understand variable update flow

   Collection sets token, folder updates if empty, then request test script runs after response to check token.

3. Step 3: Confirm correct order

   This order ensures token is set and updated before test script checks it.

4. Final Answer:

   Collection pre-request script runs first, then folder pre-request script, then request test script -> Option B

5. Quick Check:

   Pre-request scripts run before tests in order [OK]

Hint: Pre-request scripts run before tests, top-down order [OK]

Common Mistakes:

• Thinking test scripts run before pre-request scripts
• Assuming folder scripts run before collection scripts
• Believing request pre-request scripts run after tests