Why pre-request scripts prepare data in Postman - Quick Recap

Recall & Review

beginner

What is the main purpose of a pre-request script in Postman?

A pre-request script runs before the API request to prepare or modify data needed for the request, like setting variables or generating tokens.

beginner

How do pre-request scripts help in dynamic data handling?

They allow you to create or update data like timestamps, random values, or authentication tokens right before sending the request, making tests flexible and realistic.

intermediate

Why is preparing data in pre-request scripts better than hardcoding it in the request?

Because it avoids stale or repeated data, reduces manual updates, and supports automated, repeatable tests with fresh data every time.

beginner

Give an example of data commonly prepared in a pre-request script.

Generating a current timestamp or creating a unique user ID to use in the request body or headers.

intermediate

How do pre-request scripts improve test reliability?

By ensuring each request uses valid, up-to-date data, they reduce failures caused by outdated or missing information.

What does a pre-request script in Postman do?

A Sends the API request

B Runs after the request to check response

C Runs before the request to prepare data

D Generates the test report

Pre-request scripts run before the API request to prepare or modify data.

Why use pre-request scripts instead of hardcoding data?

A To make tests slower

B To skip authentication

C To ignore errors

D To avoid stale or repeated data

Pre-request scripts help avoid stale or repeated data by generating fresh data each time.

Which of these is a common use of pre-request scripts?

A Generating a timestamp

B Validating response status

C Creating test reports

D Running UI tests

Generating timestamps is a common task done in pre-request scripts.

When do pre-request scripts run in Postman?

A Before sending the request

B Only when tests fail

C During test report generation

D After the response is received

Pre-request scripts run before sending the API request.

How do pre-request scripts improve test automation?

A By manually updating data

B By preparing fresh data automatically

C By disabling tests

D By ignoring API responses

They prepare fresh data automatically, making tests repeatable and reliable.

Explain why pre-request scripts are important for preparing data in Postman.

Think about what happens before sending an API request.

Describe a real-life example where pre-request scripts help in API testing.

Imagine you need fresh data every time you test.

Practice

1. Why do pre-request scripts run before sending a request in Postman?

easy

A. To display the test results

B. To check the response status code

C. To prepare or update data needed for the request

D. To log the response time

Solution

1. Step 1: Understand the role of pre-request scripts

   Pre-request scripts run before the request is sent to prepare or update any data needed for the request.

2. Step 2: Differentiate from other script types

   Scripts that check response status or display results run after the request, not before.

3. Final Answer:

   To prepare or update data needed for the request -> Option C

4. Quick Check:

   Pre-request scripts prepare data = C [OK]

Hint: Pre-request scripts run before requests to set data [OK]

Common Mistakes:

• Confusing pre-request scripts with test scripts
• Thinking pre-request scripts check responses
• Assuming pre-request scripts run after requests

2. Which of the following is the correct way to set a variable named token in a pre-request script?

easy

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

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

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

D. pm.environment.delete('token', 'abc123');

Solution

1. Step 1: Identify the correct method to set a variable

   In Postman scripts, pm.variables.set or pm.environment.set is used to set variables. Here, pm.variables.set('token', 'abc123'); correctly sets the variable.

2. Step 2: Understand other methods

   pm.environment.get and pm.variables.get retrieve variables, not set them. pm.environment.delete removes variables.

3. Final Answer:

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

4. Quick Check:

   Set variable uses .set() method = B [OK]

Hint: Use .set() to assign variables in pre-request scripts [OK]

Common Mistakes:

• Using .get() instead of .set() to assign variables
• Confusing environment and variables methods
• Trying to delete variables when setting them

3. What will be the value of the variable timestamp after running this pre-request script?

const now = new Date().getTime();
pm.variables.set('timestamp', now);

medium

A. A number representing milliseconds since Jan 1, 1970

B. An error because pm.variables.set is incorrect

C. Undefined because now is not set

D. A string representing the current date

Solution

1. Step 1: Understand new Date().getTime()

   This returns the current time in milliseconds since January 1, 1970 (Unix epoch) as a number.

2. Step 2: Check variable assignment

   The script sets the variable timestamp to this number using pm.variables.set, which is correct syntax.

3. Final Answer:

   A number representing milliseconds since Jan 1, 1970 -> Option A

4. Quick Check:

   getTime() returns milliseconds number = D [OK]

Hint: getTime() returns milliseconds number, not string [OK]

Common Mistakes:

• Thinking getTime() returns a date string
• Assuming variable is undefined
• Confusing set() method usage

4. Identify the error in this pre-request script:

pm.environment.set('authToken', getToken());
function getToken() {
  return getToken();
}

medium

A. The function getToken is missing parentheses

B. pm.environment.set is not a valid method

C. Variables cannot be set in pre-request scripts

D. The function getToken causes infinite recursion

Solution

1. Step 1: Analyze the function call

   The script calls getToken() inside pm.environment.set('authToken', getToken()). The function getToken() returns getToken(), which calls itself again.

2. Step 2: Identify recursion problem

   This causes infinite recursion because getToken() calls itself directly, leading to a stack overflow.

3. Final Answer:

   The function getToken causes infinite recursion -> Option D

4. Quick Check:

   Function calls itself recursively = infinite recursion [OK]

Hint: Avoid recursive functions in pre-request scripts [OK]

Common Mistakes:

• Thinking pm.environment.set is invalid
• Missing that getToken calls itself recursively
• Assuming variables can't be set in pre-request scripts

5. You want to generate a random user ID before each request and store it in an environment variable userId. Which pre-request script correctly achieves this?

hard

A. const id = Math.random() * 1000;
pm.environment.get('userId', id);

B. const id = Math.floor(Math.random() * 1000);
pm.environment.set('userId', id);

C. pm.environment.set('userId', Math.random());

D. const id = Math.floor(Math.random() * 1000);
pm.environment.delete('userId');

Solution

1. Step 1: Generate a random integer ID

   Math.floor(Math.random() * 1000) generates a random whole number between 0 and 999, suitable for a user ID.

2. Step 2: Correctly set the environment variable

   pm.environment.set('userId', id); correctly stores the generated ID in the environment variable userId.

3. Final Answer:

   const id = Math.floor(Math.random() * 1000); pm.environment.set('userId', id); -> Option B

4. Quick Check:

   Use Math.floor and .set() to store random ID = A [OK]

Hint: Use Math.floor and pm.environment.set to save random IDs [OK]

Common Mistakes:

• Using .get() instead of .set() to store variables
• Not rounding random numbers to integers
• Deleting variables instead of setting them