Variable assignment in flows in Postman - Build an Automation Script

Assign and use variables in Postman request flow

Preconditions (2)

Step 1: Open the first request in the collection

Step 2: Send the request and capture a value from the JSON response (e.g., userId)

Step 3: Assign the captured value to a collection variable named 'userId'

Step 4: Open the second request in the collection

Step 5: Use the collection variable 'userId' in the URL or headers of the second request

Step 6: Send the second request

✅ Expected Result: The first request runs successfully and assigns the 'userId' variable. The second request uses the assigned 'userId' variable correctly and runs successfully.

Automation Requirements - Postman test scripts

Assertions Needed:

Verify the first request response status is 200

Verify the 'userId' variable is assigned and not empty

Verify the second request response status is 200

Best Practices:

Use pm.response.json() to parse JSON response

Use pm.collectionVariables.set() to assign variables

Use pm.collectionVariables.get() to retrieve variables

Add assertions to verify response status and variable assignment

Keep variable names clear and consistent

Automated Solution

Postman

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

const jsonData = pm.response.json();
if (jsonData.userId) {
    pm.collectionVariables.set('userId', jsonData.userId);
    pm.test('userId variable is set', () => {
        pm.expect(pm.collectionVariables.get('userId')).to.not.be.empty;
    });
} else {
    pm.test('userId exists in response', () => {
        pm.expect.fail('userId not found in response');
    });
}

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

The first request test script checks that the response status is 200, meaning the request succeeded.

It then parses the JSON response using pm.response.json() and checks if userId exists.

If userId is found, it assigns it to a collection variable named userId using pm.collectionVariables.set().

It also asserts that the variable is not empty to confirm assignment.

If userId is missing, the test fails with a clear message.

The second request test script simply verifies that the response status is 200, assuming the request URL or headers use the {{userId}} variable from the collection variables.

This approach ensures the variable is assigned and used correctly across requests in the flow.

Common Mistakes - 4 Pitfalls

Using environment variables instead of collection variables without updating the environment

Not checking if the response contains the expected key before assigning variable

Hardcoding variable values instead of capturing from response

Not adding assertions to verify variable assignment

Bonus Challenge

Now add data-driven testing by running the first request with 3 different user credentials and verify variable assignment each time

Show Hint

Practice

1. What does pm.variables.set('token', 'abc123') do in a Postman test script?

easy

A. It saves the value 'abc123' to a variable named 'token' for later use.

B. It retrieves the value of the variable 'token'.

C. It deletes the variable named 'token'.

D. It sends 'abc123' as a request header named 'token'.

Solution

1. Step 1: Understand the method pm.variables.set

   This method assigns a value to a variable in Postman scripts.

2. Step 2: Analyze the parameters

   The first parameter is the variable name 'token', the second is the value 'abc123' to store.

3. Final Answer:

   It saves the value 'abc123' to a variable named 'token' for later use. -> Option A

4. Quick Check:

   pm.variables.set saves data [OK]

Hint: Set stores data; get retrieves it [OK]

Common Mistakes:

• Confusing set with get method
• Thinking set deletes variables
• Assuming set sends data in requests

2. Which of the following is the correct syntax to assign a variable named 'userId' with value 42 in a Postman test script?

easy

A. pm.variables.get('userId', 42);

B. pm.variables.store('userId', 42);

C. pm.variables.assign('userId' = 42);

D. pm.variables.set('userId', 42);

Solution

1. Step 1: Recall the correct method for assigning variables

   The method to assign a variable is pm.variables.set(name, value).

2. Step 2: Check each option's syntax

   pm.variables.set('userId', 42); uses pm.variables.set('userId', 42); which is correct syntax.

3. Final Answer:

   pm.variables.set('userId', 42); -> Option D

4. Quick Check:

   Use pm.variables.set to assign [OK]

Hint: Set method assigns variables with (name, value) [OK]

Common Mistakes:

• Using get instead of set to assign
• Incorrect method names like assign or store
• Wrong parameter syntax with equals sign

3. Consider this Postman test script snippet:

pm.variables.set('count', 5);
pm.variables.set('count', pm.variables.get('count') + 3);
console.log(pm.variables.get('count'));

What will be printed in the console?

medium

A. 5

B. 8

C. Error

D. undefined

Solution

1. Step 1: Analyze the first assignment

   The variable 'count' is set to 5 initially.

2. Step 2: Analyze the second assignment

   It gets the current 'count' value (5), adds 3, and sets 'count' to 8.

3. Step 3: Check the console.log output

   It prints the updated value of 'count', which is 8.

4. Final Answer:

   8 -> Option B

5. Quick Check:

   5 + 3 = 8 [OK]

Hint: Get current value, add, then set updated value [OK]

Common Mistakes:

• Assuming the first value stays unchanged
• Thinking get returns undefined
• Confusing set and get usage

4. You wrote this Postman test script:

pm.variables.set('status', 'active')
pm.variables.get('status')

But the test fails because the variable 'status' is undefined. What is the likely cause?

medium

A. Variables set in one request are not available in another without environment or global scope.

B. pm.variables.get returns undefined if set is not awaited.

C. Missing semicolon after set statement causes failure.

D. Variable names cannot be strings.

Solution

1. Step 1: Understand variable scopes in Postman

   Variables set with pm.variables.set are local to the current request script and do not persist across requests.

2. Step 2: Identify why 'status' is undefined

   If you try to get 'status' in a different request without using environment or global variables, it will be undefined.

3. Final Answer:

   Variables set in one request are not available in another without environment or global scope. -> Option A

4. Quick Check:

   Local variables don't persist across requests [OK]

Hint: Use environment/global variables for cross-request data [OK]

Common Mistakes:

• Thinking semicolons affect variable persistence
• Believing get waits for set automatically
• Assuming variable names can't be strings

5. You want to save a user token from a response JSON and reuse it in the next request. Which flow correctly assigns and retrieves the token using Postman variables?

hard

A. In first request test script: pm.variables.set('token', pm.response.json().token);In next request pre-request script: const token = pm.environment.get('token');

B. In first request test script: pm.variables.set('token', pm.response.json().token);In next request pre-request script: const token = pm.variables.get('token');

C. In first request test script: pm.environment.set('token', pm.response.json().token);In next request pre-request script: const token = pm.environment.get('token');

D. In first request test script: pm.environment.set('token', pm.response.json().token);In next request pre-request script: const token = pm.variables.get('token');

Solution

1. Step 1: Identify variable scope for cross-request use

   To reuse data across requests, environment variables must be used, not local variables.

2. Step 2: Match correct set and get methods

   In first request test script: pm.environment.set('token', pm.response.json().token);
   In next request pre-request script: const token = pm.environment.get('token'); uses pm.environment.set and pm.environment.get, which correctly share data between requests.

3. Final Answer:

   Use environment variables to save and retrieve token across requests. -> Option C

4. Quick Check:

   Environment variables persist across requests [OK]

Hint: Use environment variables for data between requests [OK]

Common Mistakes:

• Using pm.variables for cross-request data
• Mixing environment and local variable methods
• Not retrieving variables in the correct scope