Dynamic URL building in Postman - Build an Automation Script

Build and test dynamic URL with query parameters in Postman

Preconditions (2)

Step 1: Open Postman and create a new GET request

Step 2: Set the base URL to https://api.example.com/items

Step 3: Add query parameters dynamically: category=books, sort=price_asc, limit=10

Step 4: Send the request

Step 5: Verify the request URL includes all query parameters correctly

Step 6: Verify the response status code is 200

Step 7: Verify the response body contains items filtered by category 'books'

✅ Expected Result: The request URL is https://api.example.com/items?category=books&sort=price_asc&limit=10, the response status code is 200, and the response body contains items filtered by category 'books'

Automation Requirements - Postman test scripts (JavaScript)

Assertions Needed:

Verify request URL contains all query parameters

Verify response status code is 200

Verify response body contains expected filtered data

Best Practices:

Use Postman environment variables for dynamic parts

Use pm.request.url.query to verify query parameters

Use pm.response.to.have.status to check status code

Use JSON parsing and assertions for response body

Keep test scripts clear and maintainable

Automated Solution

Postman

pm.test('Request URL contains all query parameters', () => {
    const url = pm.request.url.toString();
    pm.expect(url).to.include('category=books');
    pm.expect(url).to.include('sort=price_asc');
    pm.expect(url).to.include('limit=10');
});

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

pm.test('Response body contains items filtered by category books', () => {
    const jsonData = pm.response.json();
    pm.expect(jsonData).to.be.an('object');
    pm.expect(jsonData.items).to.be.an('array').that.is.not.empty;
    jsonData.items.forEach(item => {
        pm.expect(item.category).to.eql('books');
    });
});

The first test checks that the request URL includes all the expected query parameters by converting the request URL to a string and verifying each parameter is present.

The second test asserts that the response status code is 200, indicating a successful request.

The third test parses the JSON response body, ensures it contains an array of items, and verifies each item's category is 'books' to confirm filtering worked.

Using Postman built-in pm API ensures clear and maintainable test scripts.

Common Mistakes - 4 Pitfalls

Hardcoding full URL instead of using environment variables

Not verifying all query parameters in the request URL

Assuming response body structure without validation

Using pm.response.text() instead of pm.response.json() for JSON responses

Bonus Challenge

Now add data-driven testing with 3 different sets of query parameters (e.g., category=books, category=electronics, category=clothing) and verify the response accordingly

Show Hint

Practice

1. What is the main purpose of using dynamic URL building in Postman?

easy

A. To make URLs longer and more complex

B. To write URLs only once without any changes

C. To reuse URLs by inserting variables for flexibility

D. To avoid using variables in requests

Solution

1. Step 1: Understand dynamic URL building

   Dynamic URL building means using variables to create flexible URLs that can change based on input.

2. Step 2: Identify the benefit in Postman

   Using variables like {{variableName}} lets you reuse URLs easily without rewriting them for each test.

3. Final Answer:

   To reuse URLs by inserting variables for flexibility -> Option C

4. Quick Check:

   Dynamic URL building = reuse URLs with variables [OK]

Hint: Remember: variables make URLs flexible and reusable [OK]

Common Mistakes:

• Thinking dynamic URLs make URLs longer
• Believing variables are not needed in URLs
• Confusing dynamic URLs with static URLs

2. Which of the following is the correct syntax to use a variable named userId in a Postman URL?

easy

A. /api/users/%userId%

B. /api/users/$userId

C. /api/users/{userId}

D. /api/users/{{userId}}

Solution

1. Step 1: Recall Postman variable syntax

   Postman uses double curly braces {{variableName}} to insert variables in URLs.

2. Step 2: Match syntax to options

   Only /api/users/{{userId}} uses {{userId}}, which is the correct Postman syntax.

3. Final Answer:

   /api/users/{{userId}} -> Option D

4. Quick Check:

   Postman variable syntax = {{variableName}} [OK]

Hint: Use double curly braces {{}} for variables in Postman URLs [OK]

Common Mistakes:

• Using single braces or dollar signs instead of {{}}
• Confusing Postman syntax with other languages
• Forgetting to wrap variable names in curly braces

3. Given the environment variable baseUrl set to https://api.example.com and the request URL {{baseUrl}}/users/{{userId}} with userId set to 42, what is the final URL sent by Postman?

medium

A. https://api.example.com/users/42

B. https://api.example.com/users/{{userId}}

C. {{baseUrl}}/users/42

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

Solution

1. Step 1: Substitute environment variables

   Postman replaces {{baseUrl}} with its value https://api.example.com and {{userId}} with 42.

2. Step 2: Build the final URL

   After substitution, the URL becomes https://api.example.com/users/42.

3. Final Answer:

   https://api.example.com/users/42 -> Option A

4. Quick Check:

   Variable substitution = final URL with values [OK]

Hint: Replace all {{variables}} with their values before sending [OK]

Common Mistakes:

• Leaving variables unsubstituted in the URL
• Mixing variable names or values
• Ignoring environment variable settings

4. You wrote the URL {{baseUrl}/users/{{userId}} in Postman, but the request fails. What is the likely error?

medium

A. Missing closing curly brace for {{baseUrl}} variable

B. Using wrong variable name userId

C. Variables cannot be used in URLs

D. Postman does not support dynamic URLs

Solution

1. Step 1: Check variable syntax carefully

   The URL has {{baseUrl} missing a closing brace, which breaks variable substitution.

2. Step 2: Understand impact of syntax error

   Without proper braces, Postman cannot replace the variable, causing the request to fail.

3. Final Answer:

   Missing closing curly brace for {{baseUrl}} variable -> Option A

4. Quick Check:

   Correct variable syntax requires matching {{ and }} [OK]

Hint: Always count opening and closing braces in variables [OK]

Common Mistakes:

• Forgetting to close curly braces
• Assuming variable names are wrong without checking syntax
• Believing variables can't be used in URLs

5. You want to build a URL in Postman that changes the endpoint based on a variable env which can be dev or prod. Which URL correctly uses dynamic URL building to select the environment?

hard

A. https://api.example.com/env/users

B. https://api.example.com/{{env}}/users

C. https://api.example.com/${env}/users

D. https://api.example.com/{env}/users

Solution

1. Step 1: Identify correct variable syntax for environment

   Postman uses {{env}} to insert the variable value dynamically in the URL.

2. Step 2: Confirm URL structure for environment selection

   Using https://api.example.com/{{env}}/users allows switching between dev or prod endpoints easily.

3. Final Answer:

   https://api.example.com/{{env}}/users -> Option B

4. Quick Check:

   Use {{variable}} to dynamically select URL parts [OK]

Hint: Use {{env}} to switch URL parts dynamically [OK]

Common Mistakes:

• Using wrong variable syntax like ${env} or {env}
• Hardcoding environment names instead of variables
• Not placing variable in correct URL position