Looping in flows in Postman - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Postman test script loop?

Consider this Postman test script that loops through an array of user IDs and sets environment variables. What will be the value of the environment variable lastUserId after the script runs?

Postman

const userIds = [101, 102, 103];
for (let i = 0; i < userIds.length; i++) {
    pm.environment.set('lastUserId', userIds[i]);
}

A lastUserId = 102

B lastUserId = 101

C lastUserId = undefined

D lastUserId = 103

💡 Hint

Think about what happens to the variable lastUserId inside the loop on each iteration.

The loop sets lastUserId to each user ID in the array in order. After the loop finishes, the variable holds the last value assigned, which is 103.

❓ assertion

intermediate

Which assertion correctly verifies all items in a Postman response array?

You receive a JSON response with an array of user objects. You want to assert that every user has an active property set to true. Which Postman test assertion is correct?

Postman

const users = pm.response.json().users;

A pm.test('All users active', () => { pm.expect(users.some(u => u.active === true)).to.be.true; });

B pm.test('All users active', () => { pm.expect(users.every(u => u.active === true)).to.be.true; });

C pm.test('All users active', () => { pm.expect(users.find(u => u.active === false)).to.be.undefined; });

D pm.test('All users active', () => { pm.expect(users.filter(u => u.active === true).length).to.equal(users.length); });

💡 Hint

Check which method ensures every user is active.

every() returns true only if all elements satisfy the condition. Option B uses this correctly. Option B checks if some are active, which is not enough. Option B checks if any inactive user exists but is less direct. Option B counts active users but is more complex.

🔧 Debug

advanced

Why does this Postman loop not set all variables as expected?

This Postman script tries to set environment variables for each item in an array but only the last variable is set. What is the main reason?

Postman

const items = ['a', 'b', 'c'];
for (var i = 0; i < items.length; i++) {
    pm.environment.set('item', items[i]);
}

A The variable name 'item' is the same in each iteration, so it overwrites previous values.

B The loop uses 'var' instead of 'let', causing a scope error.

C pm.environment.set cannot be called inside loops.

D The array 'items' is empty, so the loop never runs.

💡 Hint

Consider how environment variables are stored and named.

Each call to pm.environment.set with the same key overwrites the previous value. To store all items, unique keys per iteration are needed.

❓ framework

advanced

How to loop through a collection of requests in Postman using the Collection Runner?

You want to run a set of requests multiple times with different data sets in Postman. Which approach correctly uses looping in the Collection Runner?

A Write a for loop inside the Pre-request Script to call pm.sendRequest multiple times for each data set.

B Manually duplicate requests in the collection for each data set and run them sequentially.

C Use a data file (CSV/JSON) with multiple rows and run the collection with the Collection Runner to loop through each data row.

D Use the Postman Console to execute the same request repeatedly by clicking run multiple times.

💡 Hint

Think about how Postman supports data-driven testing.

The Collection Runner supports looping through data files to run requests multiple times with different inputs. This is the standard way to loop through test data in Postman.

🧠 Conceptual

expert

What is the best way to handle asynchronous loops in Postman test scripts?

You need to perform multiple asynchronous API calls in a loop inside a Postman test script and wait for all to complete before continuing. Which approach correctly handles this?

A Use <code>Promise.all</code> with an array of <code>pm.sendRequest</code> promises to run all requests in parallel and await completion.

B Use a regular <code>for</code> loop with <code>pm.sendRequest</code> calls without awaiting, relying on Postman to handle concurrency.

C Postman test scripts do not support asynchronous calls; all requests must be synchronous.

D Use <code>async/await</code> inside a <code>for...of</code> loop to await each <code>pm.sendRequest</code> call sequentially.

💡 Hint

Consider how to run multiple async calls efficiently and wait for all to finish.

Using Promise.all allows running multiple pm.sendRequest calls in parallel and waiting for all to complete before proceeding. Option A runs sequentially, which is slower. Option A does not wait and may cause race conditions. Option A is incorrect as Postman supports async calls.