Generating dynamic data in Postman - Build an Automation Script

Generate dynamic user data for API request

Preconditions (2)

Step 1: Open Postman and create a new POST request to https://api.example.com/users

Step 2: In the Body tab, select raw and JSON format

Step 3: Add JSON body with fields: name, email, and phone

Step 4: Use Postman dynamic variables to generate random name, email, and phone

Step 5: Send the request

Step 6: Verify the response status is 201 Created

Step 7: Verify the response body contains the same name and email as sent

✅ Expected Result: The API accepts the dynamically generated user data and returns status 201 with the correct user details in the response body

Automation Requirements - Postman Tests (JavaScript)

Assertions Needed:

Response status code is 201

Response body contains the sent name

Response body contains the sent email

Best Practices:

Use Postman dynamic variables like {{$randomFirstName}}, {{$randomEmail}}

Write assertions in the Tests tab using pm.expect

Keep test scripts clear and maintainable

Automated Solution

Postman

pm.test('Status code is 201', function () {
    pm.response.to.have.status(201);
});

const responseJson = pm.response.json();

pm.test('Response contains sent name', function () {
    pm.expect(responseJson.name).to.eql(pm.variables.get('name'));
});

pm.test('Response contains sent email', function () {
    pm.expect(responseJson.email).to.eql(pm.variables.get('email'));
});

This test script runs after the request is sent.

First, it checks the response status is 201, meaning the user was created successfully.

Then it parses the JSON response body.

It asserts that the response's name and email fields match the values sent in the request, which are stored in Postman variables.

This ensures the API accepted the dynamic data correctly.

Common Mistakes - 3 Pitfalls

Hardcoding user data instead of using dynamic variables

Not storing dynamic data in variables for assertions

Using incorrect assertion syntax in Postman tests

Bonus Challenge

Now add data-driven testing by running the request with 3 different sets of dynamic user data automatically

Show Hint

Practice

1. What is the main purpose of generating dynamic data in Postman tests?

easy

A. To hardcode fixed values for all requests

B. To slow down the test execution

C. To make tests flexible and simulate real user input

D. To avoid using any variables in tests

Solution

1. Step 1: Understand dynamic data role

   Dynamic data allows tests to use different values each time, simulating real users.

2. Step 2: Compare options

   Only To make tests flexible and simulate real user input describes making tests flexible and realistic, which is the main goal.

3. Final Answer:

   To make tests flexible and simulate real user input -> Option C

4. Quick Check:

   Dynamic data = flexible, realistic tests [OK]

Hint: Dynamic data means changing values to mimic real users [OK]

Common Mistakes:

• Thinking dynamic data slows tests
• Confusing dynamic data with fixed values
• Ignoring the need for variable data

2. Which of the following is the correct syntax to generate a random integer between 1 and 100 in Postman using dynamic variables?

easy

A. {{random.integer(1,100)}}

B. {{randomInteger(1,100)}}

C. {{randomInt(1,100)}}

D. {{random.int(1,100)}}

Solution

1. Step 1: Recall Postman random integer syntax

   Postman uses {{random.int(min,max)}} to generate random integers.

2. Step 2: Check each option

   Only {{random.int(1,100)}} matches the correct syntax exactly.

3. Final Answer:

   {{random.int(1,100)}} -> Option D

4. Quick Check:

   Correct syntax = {{random.int(min,max)}} [OK]

Hint: Use {{random.int(min,max)}} for random integers [OK]

Common Mistakes:

• Using wrong function names like randomInt or randomInteger
• Using dot instead of function call syntax
• Missing parentheses or curly braces

3. What will be the output of the following Postman dynamic variable in a request body?

{"userId": "{{random.uuid}}"}

medium

A. {"userId": "a unique UUID string generated at runtime"}

B. {"userId": "random.uuid"} (literal string, no substitution)

C. {"userId": "123e4567-e89b-12d3-a456-426614174000"} (a fixed UUID)

D. {"userId": "{{random.uuid}}"} (variable not replaced)

Solution

1. Step 1: Understand {{random.uuid}} behavior

   This variable generates a unique UUID string each time the request runs.

2. Step 2: Analyze output options

   {"userId": "a unique UUID string generated at runtime"} correctly describes a unique UUID generated at runtime, not a fixed or literal string.

3. Final Answer:

   {"userId": "a unique UUID string generated at runtime"} -> Option A

4. Quick Check:

   {{random.uuid}} = unique UUID string [OK]

Hint: {{random.uuid}} always creates a new unique ID [OK]

Common Mistakes:

• Expecting a fixed UUID value
• Thinking variable is not replaced
• Confusing with literal string output

4. You wrote {{random.int(10,5)}} in your Postman test to generate a random number between 10 and 5. What is the issue and how to fix it?

medium

A. No issue, it works fine as is

B. The min and max values are reversed; swap them to {{random.int(5,10)}}

C. Use {{random.integer(5,10)}} instead for correct syntax

D. Remove parentheses: {{random.int 5,10}}

Solution

1. Step 1: Identify parameter order requirement

   Postman expects the first argument as min and second as max; min must be less than max.

2. Step 2: Fix reversed values

   Swapping 10 and 5 to {{random.int(5,10)}} corrects the range.

3. Final Answer:

   The min and max values are reversed; swap them to {{random.int(5,10)}} -> Option B

4. Quick Check:

   Min must be less than max in {{random.int(min,max)}} [OK]

Hint: Min value must be less than max in random.int() [OK]

Common Mistakes:

• Using reversed min and max values
• Incorrect function name random.integer
• Removing parentheses causing syntax errors

5. You want to generate a dynamic email address in Postman that always uses a random username but a fixed domain @example.com. Which of the following is the best way to do this?

hard

A. {{random.username}}@example.com

B. {{random.email}}

C. {{random.username}}@{{random.domain}}

D. {{random.email}}@example.com

Solution

1. Step 1: Understand requirement

   The username should be random, but domain fixed as '@example.com'.

2. Step 2: Evaluate options

   {{random.username}}@example.com concatenates a random username with fixed domain correctly. {{random.email}} uses full random email (domain varies). {{random.username}}@{{random.domain}} randomizes domain (not fixed). {{random.email}}@example.com appends fixed domain to full email (invalid).

3. Final Answer:

   {{random.username}}@example.com -> Option A

4. Quick Check:

   Random username + fixed domain = {{random.username}}@example.com [OK]

Hint: Combine {{random.username}} with fixed domain for custom emails [OK]

Common Mistakes:

• Using {{random.email}} which randomizes domain too
• Randomizing domain when fixed domain is needed
• Appending domain to full email causing invalid format