Response body assertions in Postman

Introduction

Response body assertions check if the data returned from an API is correct. This helps make sure the API works as expected.

When you want to verify that an API returns the right user details after login.

When checking if a product list API returns the expected number of items.

When validating that an error message appears in the response after a bad request.

When confirming that a new record was created and returned correctly by the API.

Syntax

Postman

pm.test("Test description", function () {
    let jsonData = pm.response.json();
    pm.expect(jsonData.key).to.eql(expectedValue);
});

Use pm.response.json() to parse the response body as JSON.

Use pm.expect() with to.eql() to compare values exactly.

Examples

This test checks if the response has a name field equal to "Alice".

Postman

pm.test("Check user name", function () {
    let jsonData = pm.response.json();
    pm.expect(jsonData.name).to.eql("Alice");
});

This test confirms the response has exactly 5 products in the list.

Postman

pm.test("Verify product count", function () {
    let jsonData = pm.response.json();
    pm.expect(jsonData.products.length).to.eql(5);
});

This test checks if the error message contains the text "Invalid request".

Postman

pm.test("Error message present", function () {
    let jsonData = pm.response.json();
    pm.expect(jsonData.error).to.include("Invalid request");
});

Sample Program

This test verifies that the response body contains a userId of 12345 and a status of "active".

Postman

pm.test("Response body has correct user ID and status", function () {
    let jsonData = pm.response.json();
    pm.expect(jsonData.userId).to.eql(12345);
    pm.expect(jsonData.status).to.eql("active");
});

Important Notes

Always parse the response body before making assertions.

Use clear test names to describe what you are checking.

Check for both exact matches and partial matches depending on your needs.

Summary

Response body assertions check the data returned by an API.

Use pm.response.json() to read the response body.

Write clear tests to confirm the API returns expected values.

Practice

1. What does pm.response.json() do in Postman tests?

easy

A. It parses the response body as a JSON object.

B. It sends a new request to the server.

C. It clears the response body.

D. It validates the response status code.

Solution

1. Step 1: Understand the purpose of pm.response.json()

   This function reads the response body and converts it into a JSON object for easy access.

2. Step 2: Compare with other options

   Sending requests, clearing body, or validating status are different functions, not pm.response.json().

3. Final Answer:

   It parses the response body as a JSON object. -> Option A

4. Quick Check:

   Parsing response body = A [OK]

Hint: Remember: json() reads response body as JSON [OK]

Common Mistakes:

• Confusing json() with sending requests
• Thinking json() clears data
• Mixing response body parsing with status code checks

2. Which of the following is the correct syntax to assert that the response JSON has a key status with value success in Postman?

easy

A. pm.expect(response.status).to.equal('success');

B. pm.response.json().status == 'success';

C. pm.expect(pm.response.json().status).to.eql('success');

D. pm.assert(pm.response.status == 'success');

Solution

1. Step 1: Identify correct assertion syntax in Postman

   Postman uses pm.expect() with Chai assertion style, so pm.expect(pm.response.json().status).to.eql('success'); is correct.

2. Step 2: Check other options for errors

   pm.response.json().status == 'success'; lacks assertion, C uses wrong object, D uses incorrect method.

3. Final Answer:

   pm.expect(pm.response.json().status).to.eql('success'); -> Option C

4. Quick Check:

   Use pm.expect() with to.eql() for value check [OK]

Hint: Use pm.expect() with to.eql() for JSON value checks [OK]

Common Mistakes:

• Using == instead of pm.expect() for assertions
• Referencing response.status instead of response.json().status
• Using pm.assert() which is not a Postman function

3. Given this response body:

{"user":{"id":5,"name":"Alice"}}

What will this test output?

const jsonData = pm.response.json();
pm.test("User ID is 5", () => {
  pm.expect(jsonData.user.id).to.equal(5);
});

medium

A. Test passes because user.id equals 5.

B. Test fails because user.id is not 5.

C. Test throws an error due to syntax.

D. Test is skipped because no assertion is made.

Solution

1. Step 1: Parse the response JSON

   The response has user.id = 5, so jsonData.user.id is 5.

2. Step 2: Evaluate the assertion

   The test asserts jsonData.user.id equals 5, which is true, so the test passes.

3. Final Answer:

   Test passes because user.id equals 5. -> Option A

4. Quick Check:

   Value matches assertion = Pass [OK]

Hint: Match JSON path value with expected to pass test [OK]

Common Mistakes:

• Misreading JSON structure
• Assuming test fails without checking value
• Confusing syntax errors with assertion failures

4. Identify the error in this Postman test code:

const data = pm.response.json();
pm.test("Check user name", () => {
  pm.expect(data.user.name).to.equal('Bob')
});

medium

A. Missing semicolon after assertion line.

B. No error; the test code is correct.

C. Incorrect function name; should be pm.test, not pm.tests.

D. Missing parentheses after pm.expect.

Solution

1. Step 1: Review syntax of Postman test code

   The code uses pm.test correctly, with proper arrow function and assertion syntax.

2. Step 2: Check for syntax errors

   Semicolons are optional in JavaScript; parentheses and function names are correct.

3. Final Answer:

   No error; the test code is correct. -> Option B

4. Quick Check:

   Correct syntax means no error [OK]

Hint: Check function names and parentheses carefully [OK]

Common Mistakes:

• Confusing pm.test with pm.tests
• Thinking semicolons are mandatory
• Missing parentheses in pm.expect

5. You want to assert that the response JSON array items contains an object with id equal to 10. Which test code correctly checks this in Postman?

hard

A. pm.expect(pm.response.json().items.id).to.equal(10);

B. const items = pm.response.json().items;
pm.expect(items.find(id => id === 10)).to.exist;

C. pm.expect(pm.response.json().items.includes({id:10})).to.be.true;

D. const items = pm.response.json().items;
pm.expect(items.some(item => item.id === 10)).to.be.true;

Solution

1. Step 1: Understand the response structure

   items is an array of objects; we want to check if any object has id 10.

2. Step 2: Evaluate each option

   const items = pm.response.json().items; pm.expect(items.some(item => item.id === 10)).to.be.true; uses some() to check if any item has id === 10, which is correct. pm.expect(pm.response.json().items.id).to.equal(10); wrongly accesses items.id (invalid). pm.expect(pm.response.json().items.includes({id:10})).to.be.true; tries to use includes() with an object, which won't work. const items = pm.response.json().items; pm.expect(items.find(id => id === 10)).to.exist; uses find() but the callback is incorrect (should check item.id).

3. Final Answer:

   const items = pm.response.json().items; pm.expect(items.some(item => item.id === 10)).to.be.true; -> Option D

4. Quick Check:

   Use some() with correct callback for array check [OK]

Hint: Use some() to check if array contains object with property [OK]

Common Mistakes:

• Using includes() with objects (doesn't work)
• Accessing array properties directly
• Incorrect callback function in find()