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.

Practice

1. What is the main purpose of using loops in Postman test flows?

easy

A. To create new API endpoints

B. To store environment variables permanently

C. To change the Postman interface theme

D. To repeat test steps automatically for multiple inputs

Solution

1. Step 1: Understand the role of loops in testing

   Loops allow repeating actions multiple times without manual repetition.

2. Step 2: Identify the correct purpose in Postman context

   In Postman, loops help run tests on many inputs automatically.

3. Final Answer:

   To repeat test steps automatically for multiple inputs -> Option D

4. Quick Check:

   Loops = Repeat steps [OK]

Hint: Loops repeat actions to save time [OK]

Common Mistakes:

• Thinking loops create new APIs
• Confusing loops with UI settings
• Assuming loops store variables permanently

2. Which of the following is the correct syntax to start a for loop in Postman test script?

easy

A. for i = 0; i < 5; i++ { }

B. for (let i = 0; i < 5; i++) { }

C. loop (i = 0; i < 5; i++) { }

D. foreach i in 5 { }

Solution

1. Step 1: Recall JavaScript for loop syntax

   Postman scripts use JavaScript, so the loop must follow JS syntax.

2. Step 2: Identify the correct syntax

   Correct JS for loop uses: for (let i = 0; i < 5; i++) { }

3. Final Answer:

   for (let i = 0; i < 5; i++) { } -> Option B

4. Quick Check:

   JS for loop = for (init; condition; increment) [OK]

Hint: JS loops use parentheses and braces [OK]

Common Mistakes:

• Omitting parentheses around loop conditions
• Using 'loop' or 'foreach' which are invalid in JS
• Missing 'let' or 'var' declaration

3. What will be the output in Postman console after running this script?

let sum = 0;
for (let i = 1; i <= 3; i++) {
  sum += i;
}
console.log(sum);

medium

A. 6

B. 123

C. 3

D. 0

Solution

1. Step 1: Trace the loop iterations

   i goes from 1 to 3, sum adds i each time: 0+1=1, 1+2=3, 3+3=6.

2. Step 2: Confirm final sum value

   After loop ends, sum is 6, which is printed to console.

3. Final Answer:

   6 -> Option A

4. Quick Check:

   Sum 1+2+3 = 6 [OK]

Hint: Add numbers step-by-step in loop [OK]

Common Mistakes:

• Concatenating numbers as strings instead of adding
• Stopping loop early or late
• Printing initial sum without update

4. Identify the error in this Postman test script loop:

for (let i = 0; i < 5; i++)
  console.log(i);
}

medium

A. Loop condition should be i <= 5

B. Incorrect variable declaration for i

C. Missing opening brace '{' after for loop

D. console.log cannot be used inside loops

Solution

1. Step 1: Check loop syntax

   The for loop lacks an opening brace '{' after the loop declaration.

2. Step 2: Confirm braces balance

   There is a closing brace '}' without a matching opening brace, causing syntax error.

3. Final Answer:

   Missing opening brace '{' after for loop -> Option C

4. Quick Check:

   Braces must match in loops [OK]

Hint: Always open and close braces in loops [OK]

Common Mistakes:

• Ignoring missing braces
• Changing loop condition unnecessarily
• Thinking console.log is invalid inside loops

5. You want to run a test in Postman that sends requests for each user ID in an array [101, 102, 103]. Which looping method is best to use inside the pm.sendRequest callback to handle each ID sequentially?

hard

A. Use a recursive function to send requests one after another

B. Use a forEach loop without waiting for requests to finish

C. Use a simple for loop with asynchronous calls inside

D. Use a while loop that never ends

Solution

1. Step 1: Understand asynchronous request handling

   pm.sendRequest is async; simple loops run all requests at once without waiting.

2. Step 2: Choose method to run requests sequentially

   Recursive function can wait for each request to finish before next starts, ensuring order.

3. Final Answer:

   Use a recursive function to send requests one after another -> Option A

4. Quick Check:

   Sequential async calls = recursion [OK]

Hint: Use recursion for sequential async loops [OK]

Common Mistakes:

• Using forEach which runs all requests in parallel
• Using infinite while loops causing hang
• Assuming simple for loops wait for async calls