Variable syntax ({{variable}}) in Postman - Test Execution Trace

Test Overview

This test verifies that a Postman request correctly uses the variable syntax {{variable}} to substitute environment variables in the URL and headers. It checks that the request sends with the expected values and receives a successful response.

Test Code - Postman Test Script

Postman

pm.test("Variable substitution works", function () {
    // Access environment variable
    const baseUrl = pm.environment.get("baseUrl");
    const apiKey = pm.environment.get("apiKey");

    // Construct expected URL
    const expectedUrl = `${baseUrl}/users`;

    // Check request URL uses variable substitution
    pm.expect(pm.request.url.toString()).to.eql(expectedUrl);

    // Check header uses variable substitution
    const authHeader = pm.request.headers.get("Authorization");
    pm.expect(authHeader).to.eql(`Bearer ${apiKey}`);

    // Check response status
    pm.response.to.have.status(200);
});

Execution Trace - 6 Steps

Step	Action	System State	Assertion	Result
1	Test starts	Postman environment variables 'baseUrl' and 'apiKey' are set	—	PASS
2	Postman sends request with URL containing {{baseUrl}} and header containing {{apiKey}}	Request URL is 'https://api.example.com/users', Authorization header is 'Bearer 12345abcde'	—	PASS
3	Test script retrieves environment variables 'baseUrl' and 'apiKey'	Variables retrieved: baseUrl='https://api.example.com', apiKey='12345abcde'	—	PASS
4	Test script checks that request URL matches expected URL	Request URL is 'https://api.example.com/users', expected URL is 'https://api.example.com/users'	pm.expect(pm.request.url.toString()).to.eql(expectedUrl)	PASS
5	Test script checks that Authorization header matches expected value	Authorization header is 'Bearer 12345abcde', expected is 'Bearer 12345abcde'	pm.expect(authHeader).to.eql(`Bearer ${apiKey}`)	PASS
6	Test script checks that response status is 200	Response status is 200 OK	pm.response.to.have.status(200)	PASS

Failure Scenario

Failing Condition: Environment variable 'baseUrl' or 'apiKey' is missing or not substituted correctly in the request

Execution Trace Quiz - 3 Questions

What does the test verify about the URL in the Postman request?

A That the {{baseUrl}} variable is correctly replaced with its value

B That the URL contains the literal string '{{baseUrl}}'

C That the URL is empty

D That the URL uses query parameters

Key Result

Always verify that environment variables are correctly defined and active in Postman before running tests that depend on {{variable}} substitution.

Practice

1. What is the correct way to use a variable named userId in a Postman request URL?

easy

A. Use $userId in the URL to insert the variable value.

B. Use [userId] in the URL to insert the variable value.

C. Use {{userId}} in the URL to insert the variable value.

D. Use userId directly without any special syntax.

Solution

1. Step 1: Understand Postman variable syntax

   Postman uses double curly braces {{variable}} to insert variable values dynamically.

2. Step 2: Apply syntax to the variable userId

   To use the variable userId, you write {{userId}} in the request URL or body.

3. Final Answer:

   Use {{userId}} in the URL to insert the variable value. -> Option C

4. Quick Check:

   Variable syntax = {{variable}} [OK]

Hint: Remember variables always use double curly braces {{}} [OK]

Common Mistakes:

• Using single brackets or dollar sign instead of {{}}
• Writing variable name without any braces
• Confusing variable syntax with other languages

2. Which of the following is the correct syntax to reference a variable named token in Postman?

easy

A. {token}

B. {{token}}

C. [[token]]

D. $token

Solution

1. Step 1: Recall Postman variable syntax rules

   Postman requires variables to be wrapped in double curly braces to be recognized.

2. Step 2: Match the correct syntax for variable token

   The correct syntax is {{token}}, which tells Postman to replace it with the variable's value.

3. Final Answer:

   {{token}} -> Option B

4. Quick Check:

   Variable reference = {{variable}} [OK]

Hint: Always use double curly braces {{}} for variables [OK]

Common Mistakes:

• Using single braces or brackets
• Using dollar sign prefix
• Forgetting braces entirely

3. Given the environment variable baseUrl is set to https://api.example.com, what will be the full URL when the request uses {{baseUrl}}/users?

medium

A. https://api.example.comusers

B. {{baseUrl}}/users

C. https://api.example.com{{baseUrl}}/users

D. https://api.example.com/users

Solution

1. Step 1: Understand variable substitution in Postman

   Postman replaces {{baseUrl}} with its set value before sending the request.

2. Step 2: Substitute {{baseUrl}} with its value

   Since baseUrl is https://api.example.com, the URL becomes https://api.example.com/users.

3. Final Answer:

   https://api.example.com/users -> Option D

4. Quick Check:

   Variable replaced URL = https://api.example.com/users [OK]

Hint: Variables replace exactly with their set values [OK]

Common Mistakes:

• Not replacing variable and leaving {{baseUrl}} as is
• Concatenating variable value incorrectly
• Missing slash between baseUrl and path

4. You wrote Authorization: Bearer {token} in the headers, but the token is not replaced. What is the error?

medium

A. Variable syntax is incorrect; should be {{token}}.

B. Token variable is not set anywhere.

C. Bearer keyword is missing.

D. Headers do not support variables.

Solution

1. Step 1: Check the variable syntax in the header

   The header uses {token} which is missing one pair of curly braces.

2. Step 2: Correct the syntax to {{token}}

   Postman requires double curly braces to recognize variables, so it should be Authorization: Bearer {{token}}.

3. Final Answer:

   Variable syntax is incorrect; should be {{token}}. -> Option A

4. Quick Check:

   Correct variable syntax = {{variable}} [OK]

Hint: Always use double curly braces {{}} for variables in headers too [OK]

Common Mistakes:

• Using single braces instead of double
• Assuming variables auto-replace without braces
• Not setting the variable value before use

5. You want to reuse a variable sessionId inside a JSON body and a header in Postman. Which is the best practice to ensure it works correctly?

hard

A. Set sessionId as an environment variable and use {{sessionId}} in both places.

B. Write sessionId value directly in JSON and header without variables.

C. Use different variable syntaxes in JSON and header for safety.

D. Set sessionId only in the header; JSON will inherit it automatically.

Solution

1. Step 1: Understand variable scope and reuse in Postman

   Environment variables are accessible throughout the request, including headers and body.

2. Step 2: Use consistent variable syntax {{sessionId}} in both JSON body and header

   This ensures Postman replaces the variable correctly wherever it appears.

3. Final Answer:

   Set sessionId as an environment variable and use {{sessionId}} in both places. -> Option A

4. Quick Check:

   Use environment variables + {{variable}} syntax for reuse [OK]

Hint: Set once as environment variable, use {{variable}} everywhere [OK]

Common Mistakes:

• Hardcoding values instead of variables
• Using inconsistent variable syntax
• Assuming variables auto-share without setting scope