Using Chai assertion library in Postman - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ assertion

intermediate

Identify the correct Chai assertion for checking response status

You want to verify that the HTTP response status code is exactly 200 using Chai in Postman tests. Which assertion is correct?

Postman

pm.test('Status code is 200', function () {
    pm.response.to.have.status(200);
});

A pm.expect(pm.response.code).to.equal(200);

B pm.expect(pm.response.status).to.eql(200);

C pm.expect(pm.response.statusCode).to.be(200);

D pm.expect(pm.response.code).to.be.equalTo(200);

💡 Hint

Check the exact property name for status code in Postman response object.

In Postman, pm.response.code holds the numeric status code. The correct Chai assertion to check equality is to.equal(200). Other options use incorrect property names or invalid assertion methods.

❓ Predict Output

intermediate

What is the test result of this Chai assertion?

Given the response JSON body: {"success": true, "count": 5}, what will be the result of this test in Postman?

Postman

pm.test('Check success and count', function () {
    var jsonData = pm.response.json();
    pm.expect(jsonData.success).to.be.true;
    pm.expect(jsonData.count).to.be.above(3);
});

A Test fails because success is not a boolean.

B Test fails because count is not above 5.

C Test fails due to syntax error in assertion.

D Test passes because success is true and count is 5 which is above 3.

💡 Hint

Check the values in the JSON and the assertion conditions carefully.

The JSON has success: true and count: 5. The assertions check if success is true and count is greater than 3, both conditions are met, so the test passes.

❓ locator

advanced

Choose the best way to assert a nested JSON property exists

You receive this JSON response: {"user": {"id": 123, "profile": {"name": "Alice"}}}. Which Chai assertion correctly verifies that the 'name' property exists inside 'profile'?

Postman

var jsonData = pm.response.json();

A pm.expect(jsonData.user.profile).to.have.property('name');

B pm.expect(jsonData.user['profile.name']).to.exist;

C pm.expect(jsonData.user.profile.name).to.exist;

D pm.expect(jsonData.user).to.have.property('profile.name');

💡 Hint

Check how to assert nested properties with Chai's 'property' method.

Option A correctly asserts that the 'profile' object has a property 'name'. Option A tries to access nested property as a string which is invalid. Option A checks existence of the value but not property presence. Option A uses wrong key syntax.

🔧 Debug

advanced

Find the cause of this failing Chai assertion

This Postman test fails with an error: "TypeError: Cannot read property 'length' of undefined". What is the likely cause?

Postman

pm.test('Array length check', function () {
    var jsonData = pm.response.json();
    pm.expect(jsonData.items.length).to.be.above(0);
});

A The 'length' property is not a valid Chai assertion.

B The 'items' property is missing or undefined in the response JSON.

C The 'to.be.above' method is used incorrectly.

D The pm.response.json() method returns a string, not an object.

💡 Hint

Check if the property you access exists before using its attributes.

The error means jsonData.items is undefined, so accessing length fails. This usually happens if the response JSON does not have an 'items' property.

❓ framework

expert

Which Chai assertion style is used in Postman tests by default?

Postman supports multiple Chai assertion styles. Which style is the default and recommended for writing tests in Postman scripts?

A Should style (e.g., response.should.have.status(200))

B Assert style (e.g., assert.equal(response.status, 200))

C Expect style (e.g., expect(response.code).to.equal(200))

D Verify style (e.g., verify(response.status === 200))

💡 Hint

Look at common examples in Postman test scripts.

Postman uses the Expect style of Chai assertions by default. The 'should' and 'assert' styles are supported by Chai but not the default in Postman. 'Verify' style does not exist in Chai.

Practice

1. What is the main purpose of using the Chai assertion library in Postman tests?

easy

A. To create user interface elements

B. To write clear and readable checks for API responses

C. To send HTTP requests faster

D. To store environment variables

Solution

1. Step 1: Understand Chai's role in testing

   Chai is used to write assertions that check if API responses meet expectations.

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

   In Postman, Chai helps create readable tests that verify API behavior.

3. Final Answer:

   To write clear and readable checks for API responses -> Option B

4. Quick Check:

   Chai assertions = readable API checks [OK]

Hint: Chai is for checking API results clearly [OK]

Common Mistakes:

• Confusing Chai with request sending
• Thinking Chai creates UI elements
• Mixing Chai with environment variable storage

2. Which of the following is the correct syntax to assert that the response status code is 200 using Chai in Postman?

easy

A. pm.expect(response.code).to.equal(200);

B. pm.expect(pm.response.status).to.equal(200);

C. pm.expect(pm.response.code).to.equal(200);

D. pm.expect(response.status).to.be(200);

Solution

1. Step 1: Identify the correct Postman response object

   The response object in Postman is accessed via pm.response.

2. Step 2: Use Chai syntax to check status code

   The correct Chai assertion is pm.expect(pm.response.code).to.equal(200);.

3. Final Answer:

   pm.expect(pm.response.code).to.equal(200); -> Option C

4. Quick Check:

   Status code check uses pm.response.code [OK]

Hint: Use pm.response.code with to.equal for status [OK]

Common Mistakes:

• Using wrong object like response.code
• Using to.be instead of to.equal
• Missing pm.response prefix

3. Given this Postman test code:

pm.test('Check response body', () => {
  pm.expect(pm.response.text()).to.include('success');
});

What will happen if the response body is 'Operation was successful'?

medium

A. Test will pass only if response code is 200

B. Test will fail because 'success' is not exactly matched

C. Test will throw a syntax error

D. Test will pass because 'success' is included in the response

Solution

1. Step 1: Understand the assertion used

   The assertion checks if the response text includes the substring 'success'.

2. Step 2: Check if 'success' is in 'Operation was successful'

   The word 'successful' contains 'success' as a substring, so the assertion passes.

3. Final Answer:

   Test will pass because 'success' is included in the response -> Option D

4. Quick Check:

   Substring check includes 'success' [OK]

Hint: Include checks pass if substring exists anywhere [OK]

Common Mistakes:

• Expecting exact match instead of substring
• Confusing syntax error with assertion failure
• Assuming status code affects this test

4. Identify the error in this Postman test code snippet:

pm.test('Status is 404', () => {
  pm.expect(pm.response.status).to.equal(404);
});

medium

A. pm.response.status is not the correct property for status code

B. to.equal should be to.be.equal

C. pm.test should be pm.expect

D. Missing semicolon after pm.test

Solution

1. Step 1: Check the property used for status code

   The correct property for status code in Postman is pm.response.code, not pm.response.status.

2. Step 2: Confirm Chai syntax correctness

   The to.equal syntax is correct and pm.test is used properly.

3. Final Answer:

   pm.response.status is not the correct property for status code -> Option A

4. Quick Check:

   Status code property is pm.response.code [OK]

Hint: Use pm.response.code for status, not pm.response.status [OK]

Common Mistakes:

• Using pm.response.status instead of pm.response.code
• Adding unnecessary 'to.be' in assertion
• Confusing pm.test with pm.expect

5. You want to write a Postman test that asserts the JSON response has a property userId with a value greater than 100. Which code snippet correctly uses Chai assertions to do this?

hard

A. pm.test('userId > 100', () => {
const jsonData = pm.response.json();
pm.expect(jsonData.userId).to.be.above(100);
});

B. pm.test('userId > 100', () => {
const jsonData = pm.response.json();
pm.expect(jsonData.userId).to.equal(100);
});

C. pm.test('userId > 100', () => {
pm.expect(pm.response.text()).to.include('userId > 100');
});

D. pm.test('userId > 100', () => {
pm.expect(pm.response.code).to.be.above(100);
});

Solution

1. Step 1: Parse JSON response correctly

   Use pm.response.json() to get the response as an object.

2. Step 2: Use Chai's 'above' assertion on userId property

   Check that jsonData.userId is greater than 100 with to.be.above(100).

3. Final Answer:

   pm.test('userId > 100', () => { const jsonData = pm.response.json(); pm.expect(jsonData.userId).to.be.above(100); }); -> Option A

4. Quick Check:

   Parse JSON then assert property above value [OK]

Hint: Parse JSON then use to.be.above for numeric checks [OK]

Common Mistakes:

• Using to.equal instead of to.be.above
• Checking response text instead of JSON property
• Checking status code instead of userId