Local variables in Postman - Build an Automation Script

Verify usage of local variables in Postman test script

Preconditions (2)

Step 1: Open the GET request in Postman

Step 2: Go to the Tests tab

Step 3: Declare a local variable named 'responseTime' and assign it the value of pm.response.responseTime

Step 4: Write an assertion to check that 'responseTime' is less than 2000 milliseconds

Step 5: Send the request

Step 6: Observe the test results

✅ Expected Result: The test passes if the response time is less than 2000 ms, confirming the local variable 'responseTime' was correctly used in the test script

Automation Requirements - Postman Sandbox JavaScript

Assertions Needed:

Assert that the local variable 'responseTime' is less than 2000

Best Practices:

Use local variables inside the test script scope

Use pm.response object to access response details

Use pm.test and pm.expect for assertions

Automated Solution

Postman

pm.test('Response time is less than 2000ms', () => {
    let responseTime = pm.response.responseTime;
    pm.expect(responseTime).to.be.below(2000);
});

This test script declares a local variable responseTime inside the test function. It assigns the response time from pm.response.responseTime. Then it asserts that this value is below 2000 milliseconds using pm.expect. This shows how to use local variables in Postman test scripts to store and reuse response data within the test scope.

Common Mistakes - 3 Pitfalls

Declaring variables outside the test function and expecting them to persist across requests

Using global or environment variables instead of local variables for temporary data

Not using pm.expect for assertions and instead using console.log to check values

Bonus Challenge

Now add tests to check that the response status code is 200 and the response time is less than 2000ms using local variables

Show Hint

Practice

1. What is the main purpose of local variables in Postman?

easy

A. To create global environment settings

B. To save data permanently across all requests

C. To share data between different collections

D. To store data only during a single request execution

Solution

1. Step 1: Understand local variable scope

   Local variables exist only during the execution of one request and are not saved beyond that.

2. Step 2: Compare with other variable types

   Global or environment variables persist beyond one request, unlike local variables.

3. Final Answer:

   To store data only during a single request execution -> Option D

4. Quick Check:

   Local variables = single request scope [OK]

Hint: Local variables last only during one request [OK]

Common Mistakes:

• Confusing local variables with global variables
• Thinking local variables persist across requests
• Assuming local variables share data between collections

2. Which of the following is the correct syntax to set a local variable named token with value abc123 in Postman?

easy

A. pm.local.set('token', 'abc123');

B. pm.environment.set('token', 'abc123');

C. pm.variables.set('token', 'abc123');

D. pm.globals.set('token', 'abc123');

Solution

1. Step 1: Identify the correct method for local variables

   Local variables use pm.variables.set to assign values.

2. Step 2: Check other options for correctness

   pm.environment.set and pm.globals.set set environment and global variables, not local. pm.local.set is invalid.

3. Final Answer:

   pm.variables.set('token', 'abc123'); -> Option C

4. Quick Check:

   Set local variable = pm.variables.set [OK]

Hint: Use pm.variables.set() for local variables [OK]

Common Mistakes:

• Using pm.environment.set instead of pm.variables.set
• Trying to use pm.local.set which does not exist
• Confusing global and local variable methods

3. Consider this Postman test script:

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. 8

B. 5

C. Error: Cannot add number to undefined

D. null

Solution

1. Step 1: Set initial local variable 'count'

   The first line sets 'count' to 5.

2. Step 2: Increment 'count' by 3

   The second line gets 'count' (5), adds 3, and sets it back to 8.

3. Step 3: Output the updated value

   The console.log prints the current value of 'count', which is 8.

4. Final Answer:

   8 -> Option A

5. Quick Check:

   5 + 3 = 8 [OK]

Hint: Get then set to update local variable value [OK]

Common Mistakes:

• Assuming the variable does not update
• Expecting an error due to type mismatch
• Confusing local with environment variables

4. You wrote this Postman script:

pm.variables.set('user', 'Alice');
console.log(pm.variables.get('username'));

What is the problem here?

medium

A. Variable 'username' was never set, so get returns undefined

B. Syntax error in pm.variables.set method

C. Local variables cannot be logged to console

D. pm.variables.get requires two arguments

Solution

1. Step 1: Check variable names used

   The script sets 'user' but tries to get 'username', which was never set.

2. Step 2: Understand get behavior for unset variables

   Getting an unset local variable returns undefined, no error occurs.

3. Final Answer:

   Variable 'username' was never set, so get returns undefined -> Option A

4. Quick Check:

   Unset variable get = undefined [OK]

Hint: Check variable names carefully for typos [OK]

Common Mistakes:

• Assuming syntax error when variable name mismatches
• Thinking pm.variables.get needs two arguments
• Believing console.log cannot show local variables

5. You want to store a temporary token during a request and use it in multiple tests within that request. Which approach correctly uses local variables to achieve this?

hard

A. Set the token with pm.environment.set('token', 'abc') and get it with pm.variables.get('token')

B. Set the token once with pm.variables.set('token', 'abc') and get it in tests with pm.variables.get('token')

C. Set the token with pm.variables.set('token', 'abc') but cannot access it in other tests

D. Set the token with pm.globals.set('token', 'abc') and get it with pm.variables.get('token')

Solution

1. Step 1: Understand local variable scope within one request

   Local variables set with pm.variables.set are accessible throughout the request execution, including multiple tests.

2. Step 2: Verify correct get method usage

   Use pm.variables.get to retrieve the local variable value within the same request.

3. Step 3: Check other options for scope mismatch

   Environment and global variables persist beyond one request and are not local. Also, local variables are accessible across tests in the same request.

4. Final Answer:

   Set the token once with pm.variables.set('token', 'abc') and get it in tests with pm.variables.get('token') -> Option B

5. Quick Check:

   Local variable set/get works within one request [OK]

Hint: Use pm.variables.set/get to share data within one request [OK]

Common Mistakes:

• Using environment or global variables instead of local
• Thinking local variables cannot be shared between tests in one request
• Mixing set and get methods from different scopes