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.