Global variables in Postman - Build an Automation Script

Verify setting and using global variables in Postman

Preconditions (2)

Step 1: Open Postman and create a new request

Step 2: Set the request method to GET and the URL to https://postman-echo.com/get

Step 3: In the Pre-request Script tab, add code to set a global variable named 'token' with value '12345abcde'

Step 4: Send the request

Step 5: In the Tests tab, add code to verify that the global variable 'token' exists and its value is '12345abcde'

Step 6: Send the request again to execute the test script

Step 7: Open the Globals section in Postman to verify the variable 'token' is set with the correct value

✅ Expected Result: The global variable 'token' is set to '12345abcde' before the request, the test script confirms the variable exists with the correct value, and the Globals section shows the variable with the expected value.

Automation Requirements - Postman test scripts (JavaScript)

Assertions Needed:

Assert global variable 'token' exists

Assert global variable 'token' value equals '12345abcde'

Best Practices:

Use pm.globals.set() to set global variables

Use pm.globals.get() to retrieve global variables

Use pm.test() and pm.expect() for assertions

Keep scripts clear and maintainable

Automated Solution

Postman

/* Pre-request Script */
pm.globals.set('token', '12345abcde');

/* Tests Script */
pm.test('Global variable token is set', () => {
    const token = pm.globals.get('token');
    pm.expect(token).to.not.be.undefined;
    pm.expect(token).to.eql('12345abcde');
});

In the Pre-request Script, pm.globals.set('token', '12345abcde') sets the global variable before the request runs.

In the Tests tab, pm.test defines a test named 'Global variable token is set'. Inside, pm.globals.get('token') retrieves the variable. The assertions check that the variable exists and its value matches '12345abcde'.

This approach ensures the variable is set before the request and verified after the response, following Postman's scripting best practices.

Common Mistakes - 3 Pitfalls

{'mistake': 'Using environment variables instead of global variables when global scope is needed', 'why_bad': "Environment variables are limited to a specific environment and won't be accessible globally across all collections or requests.", 'correct_approach': 'Use pm.globals.set() and pm.globals.get() to manage variables that need to be accessible everywhere.'}

{'mistake': 'Setting global variables in the Tests script instead of Pre-request Script', 'why_bad': "Tests run after the request, so the variable won't be set before the request executes, causing dependent requests to fail.", 'correct_approach': 'Set global variables in the Pre-request Script to ensure they exist before the request runs.'}

Not checking if the global variable exists before using it

Bonus Challenge

Now add data-driven testing by setting the global variable 'token' with three different values and verify each in separate requests.

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