Using Chai assertion library in Postman - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the Chai assertion library used for in Postman tests?

Chai is used to write clear and readable assertions to check if API responses meet expected conditions during Postman tests.

beginner

How do you write a basic assertion to check if a response status code is 200 using Chai in Postman?

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

intermediate

What does the Chai assertion 'expect(response).to.have.property("name")' check for?

It checks that the response object has a property called "name".

intermediate

Explain the difference between 'expect' and 'assert' styles in Chai.

Both are assertion styles in Chai. 'expect' reads like natural language (e.g., expect(value).to.equal(5)), while 'assert' uses functions (e.g., assert.equal(value, 5)). Both check conditions but differ in syntax.

beginner

How can you check if a JSON response body contains a specific string using Chai in Postman?

Use: pm.test('Body contains string', function () { pm.expect(pm.response.text()).to.include('expected string'); });

Which Chai assertion checks if a response status is 404?

A pm.response.status(404);

B pm.response.to.be.status(404);

C pm.response.to.have.status(404);

D pm.response.has.status(404);

The correct syntax to check status code is pm.response.to.have.status(404);

What does this assertion check? pm.expect(responseJson.success).to.be.true;

A That responseJson.success is a string

B That responseJson.success is true

C That responseJson.success is false

D That responseJson.success exists

It checks that the success property in responseJson is exactly true.

Which Chai style uses natural language syntax?

A expect

B assert

C should

D verify

'expect' style reads like natural language, e.g., expect(value).to.equal(5).

How do you check if response body contains the word 'success'?

A pm.expect(pm.response.text()).to.include('success');

B pm.response.to.have.body('success');

C pm.expect(pm.response.body).to.have.string('success');

D pm.response.body.includes('success');

pm.expect(pm.response.text()).to.include('success'); correctly checks if the response text contains 'success'.

What is the purpose of pm.test() in Postman tests?

A To set environment variables

B To send an API request

C To log response data

D To define a test case with a name and function

pm.test() defines a test with a descriptive name and a function containing assertions.

Describe how to write a Chai assertion in Postman to verify the response status code and a JSON property value.

Think about checking status first, then accessing JSON body and asserting a property.

Explain the difference between 'expect' and 'assert' styles in Chai and when you might prefer one over the other.

Consider how each style reads and how easy it is to understand.

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