Environment variables in Postman - Build an Automation Script

Verify usage of environment variables in Postman request

Preconditions (2)

Step 1: Select the environment 'TestEnv' in Postman

Step 2: Create a new GET request with URL '{{baseUrl}}/posts/1'

Step 3: Send the request

Step 4: Observe the response status code and body

✅ Expected Result: The request is sent to 'https://jsonplaceholder.typicode.com/posts/1' and the response status code is 200 with a valid JSON body containing post details

Automation Requirements - Postman/Newman

Assertions Needed:

Verify response status code is 200

Verify response body contains userId, id, title, and body fields

Best Practices:

Use environment variables for base URLs and dynamic data

Use pm.expect assertions for validation

Keep tests independent and clear

Automated Solution

Postman

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

const jsonData = pm.response.json();
pm.test('Response has userId', () => {
    pm.expect(jsonData).to.have.property('userId');
});
pm.test('Response has id', () => {
    pm.expect(jsonData).to.have.property('id');
});
pm.test('Response has title', () => {
    pm.expect(jsonData).to.have.property('title');
});
pm.test('Response has body', () => {
    pm.expect(jsonData).to.have.property('body');
});

This script is written in Postman test tab using pm API.

First, it checks if the response status code is 200, meaning the request was successful.

Then, it parses the response JSON and verifies that the expected fields userId, id, title, and body exist in the response.

Using environment variable {{baseUrl}} in the request URL allows easy switching of target servers without changing the test code.

Common Mistakes - 3 Pitfalls

Hardcoding the full URL instead of using environment variables

Not checking the response status code before validating response body

Using incorrect syntax for pm.expect assertions

Bonus Challenge

Now add data-driven testing by running the same request with environment variables for post IDs 1, 2, and 3

Show Hint

Practice

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

easy

A. To store reusable values that can be used across multiple requests

B. To write test assertions for API responses

C. To create new API endpoints automatically

D. To generate random data for requests

Solution

1. Step 1: Understand environment variables role

   Environment variables hold values like URLs or tokens that you reuse in many requests.

2. Step 2: Compare with other options

   Writing tests or generating data are different features, not the main use of environment variables.

3. Final Answer:

   To store reusable values that can be used across multiple requests -> Option A

4. Quick Check:

   Environment variables = reusable values [OK]

Hint: Environment variables hold reusable data for requests [OK]

Common Mistakes:

• Confusing environment variables with test scripts
• Thinking environment variables create endpoints
• Assuming they generate random data automatically

2. Which of the following is the correct way to set an environment variable named token to abc123 in a Postman test script?

easy

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

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

C. pm.environment.get('token', 'abc123');

D. pm.setEnvironment('token', 'abc123');

Solution

1. Step 1: Identify correct method to set environment variable

   Postman uses pm.environment.set(key, value) to set environment variables.

2. Step 2: Check other options for correctness

   pm.variables.set sets local variables, pm.environment.get is for getting values, and pm.setEnvironment is not a valid method.

3. Final Answer:

   pm.environment.set('token', 'abc123'); -> Option A

4. Quick Check:

   Set env var = pm.environment.set(key, value) [OK]

Hint: Use pm.environment.set() to assign environment variables [OK]

Common Mistakes:

• Using pm.environment.get() to set variables
• Confusing pm.variables.set() with environment variables
• Using non-existent methods like pm.setEnvironment()

3. Given the following Postman test script, what will be the value of the environment variable userId after execution?

pm.environment.set('userId', 10);
pm.environment.set('userId', Number(pm.environment.get('userId')) + 5);

medium

A. Error

B. 10

C. undefined

D. 15

Solution

1. Step 1: Analyze first line setting userId

   The first line sets userId to 10.

2. Step 2: Analyze second line updating userId

   The second line gets current userId (10), adds 5, and sets it back, so userId becomes 15.

3. Final Answer:

   15 -> Option D

4. Quick Check:

   10 + 5 = 15 [OK]

Hint: Get then set adds values correctly [OK]

Common Mistakes:

• Assuming variable stays 10 after second line
• Thinking get returns undefined initially
• Expecting a runtime error

4. You wrote this Postman script to remove an environment variable sessionId but it does not work:

pm.environment.delete('sessionId');

What is the correct way to delete an environment variable?

medium

A. pm.environment.remove('sessionId');

B. pm.environment.unset('sessionId');

C. pm.environment.clear('sessionId');

D. pm.environment.deleteVariable('sessionId');

Solution

1. Step 1: Identify correct method to delete environment variable

   Postman uses pm.environment.unset(key) to remove environment variables.

2. Step 2: Check why original code fails

   pm.environment.delete() is not a valid method, so it does not remove the variable.

3. Final Answer:

   pm.environment.unset('sessionId'); -> Option B

4. Quick Check:

   Delete env var = pm.environment.unset(key) [OK]

Hint: Use pm.environment.unset() to remove variables [OK]

Common Mistakes:

• Using pm.environment.delete() which is invalid
• Trying pm.environment.remove() or clear() which don't exist for single variables
• Confusing with non-existent deleteVariable()

5. You want to run the same Postman collection on two different servers: dev and prod. Which is the best way to use environment variables to switch the base URL without changing the request code?

hard

A. Use global variables to store the URLs and change them before each run

B. Hardcode the server URL in each request and manually change it before running

C. Create two environments with a variable baseUrl set to each server URL, then select the environment before running

D. Write separate collections for dev and prod with different URLs

Solution

1. Step 1: Understand environment variables for different setups

   Creating separate environments with baseUrl variables allows easy switching without code changes.

2. Step 2: Compare other options

   Hardcoding or separate collections cause manual errors and duplication; global variables are less flexible for multiple setups.

3. Final Answer:

   Create two environments with a variable baseUrl set to each server URL, then select the environment before running -> Option C

4. Quick Check:

   Use environments to switch URLs easily [OK]

Hint: Use separate environments with baseUrl variables [OK]

Common Mistakes:

• Hardcoding URLs in requests
• Using global variables instead of environments
• Creating duplicate collections for each server