POST request in Postman

Introduction

A POST request sends data to a server to create or update something. It helps test if the server accepts and processes data correctly.

When you want to add a new user to a website.

When submitting a form with information like name and email.

When uploading a file or sending data to a server.

When testing if the server saves data correctly after receiving it.

When checking how the server responds to new data inputs.

Syntax

Postman

POST /endpoint HTTP/1.1
Host: example.com
Content-Type: application/json

{
  "key": "value"
}

The first line shows the POST method and the URL endpoint.

The body contains the data sent, often in JSON format.

Examples

This sends new user data to create a user named Alice.

Postman

POST /users HTTP/1.1
Host: api.example.com
Content-Type: application/json

{
  "name": "Alice",
  "email": "[e-mail]"
}

This sends login data using form encoding.

Postman

POST /login HTTP/1.1
Host: api.example.com
Content-Type: application/x-www-form-urlencoded

username=bob&password=1234

Sample Program

This example sends a POST request to create a new post with title, body, and userId.

Postman

POST https://jsonplaceholder.typicode.com/posts
Content-Type: application/json

{
  "title": "foo",
  "body": "bar",
  "userId": 1
}

Important Notes

Always set the correct Content-Type header to tell the server the data format.

POST requests usually change data on the server, so use them carefully in tests.

Check the server response to confirm the data was accepted and processed.

Summary

POST requests send data to a server to create or update resources.

They include a body with data, often in JSON format.

Testing POST requests helps ensure servers handle data correctly.

Practice

1. What is the main purpose of a POST request in API testing?

easy

A. To send data to the server to create or update a resource

B. To retrieve data from the server without changing it

C. To delete a resource from the server

D. To check the server status without sending data

Solution

1. Step 1: Understand HTTP methods

   HTTP methods define actions: GET retrieves data, POST sends data to create or update resources.

2. Step 2: Identify POST request purpose

   POST requests include a body with data to be processed by the server, usually creating or updating resources.

3. Final Answer:

   To send data to the server to create or update a resource -> Option A

4. Quick Check:

   POST = send data to create/update [OK]

Hint: POST sends data to server to create or update [OK]

Common Mistakes:

• Confusing POST with GET which only retrieves data
• Thinking POST deletes data instead of creating/updating
• Assuming POST does not send a request body

2. Which of the following is the correct way to set the body of a POST request in Postman using JSON?

easy

A. Select 'Headers' tab and add JSON data as header values

B. Select 'Params' tab and enter JSON data as key-value pairs

C. Select 'Authorization' tab and paste JSON data

D. Select 'Body' tab, choose 'raw', then select 'JSON' from dropdown and enter JSON data

Solution

1. Step 1: Locate body settings in Postman

   In Postman, the 'Body' tab is used to send data with POST requests.

2. Step 2: Choose raw and JSON format

   Within 'Body', selecting 'raw' and then 'JSON' allows entering JSON formatted data correctly.

3. Final Answer:

   Select 'Body' tab, choose 'raw', then select 'JSON' from dropdown and enter JSON data -> Option D

4. Quick Check:

   Body tab + raw + JSON = correct POST body setup [OK]

Hint: Use Body > raw > JSON to send JSON data [OK]

Common Mistakes:

• Entering JSON in Params tab which is for URL parameters
• Putting JSON data in Headers which is for metadata
• Confusing Authorization tab with body data input

3. Given this Postman test script for a POST request response:

pm.test('Status code is 201', () => {
  pm.response.to.have.status(201);
});
pm.test('Response has userId', () => {
  const jsonData = pm.response.json();
  pm.expect(jsonData).to.have.property('userId');
});

What will happen if the server responds with status 200 and no userId in the JSON?

medium

A. Both tests fail because status is not 201 and userId is missing

B. First test passes, second test fails

C. Both tests pass regardless of response

D. First test fails, second test passes

Solution

1. Step 1: Check status code test

   The first test expects status 201 but server returns 200, so this test fails.

2. Step 2: Check userId property test

   The second test expects 'userId' property in JSON response, but it's missing, so this test also fails.

3. Final Answer:

   Both tests fail because status is not 201 and userId is missing -> Option A

4. Quick Check:

   Status 201 + userId present = pass; else fail [OK]

Hint: Check both status and JSON properties carefully [OK]

Common Mistakes:

• Assuming status 200 passes when test expects 201
• Ignoring missing JSON properties in assertions
• Thinking tests pass without matching conditions

4. You wrote this Postman test for a POST request:

pm.test('Check success message', () => {
  pm.expect(pm.response.json().message).to.eql('Success');
});

But the test always fails with error TypeError: Cannot read property 'message' of undefined. What is the most likely cause?

medium

A. The server returned status 404

B. The test syntax is incorrect

C. Response body is empty or not valid JSON

D. The Postman app is outdated

Solution

1. Step 1: Understand the error message

   The error means pm.response.json() returned undefined, so accessing .message fails.

2. Step 2: Identify cause of undefined JSON

   This usually happens if response body is empty or not valid JSON, so parsing fails.

3. Final Answer:

   Response body is empty or not valid JSON -> Option C

4. Quick Check:

   Empty or invalid JSON causes undefined error [OK]

Hint: Check if response body is valid JSON before accessing properties [OK]

Common Mistakes:

• Blaming test syntax instead of response content
• Ignoring server status codes affecting response body
• Assuming Postman app version causes this error

5. You want to test a POST request that creates a new user with fields name and email. Which Postman test script correctly verifies the server response includes the same email you sent and a status code 201?

hard

A. pm.test('Status 201 and email match', () => {
pm.response.to.have.status(201);
const res = pm.response.json();
pm.expect(res.email).to.eql(pm.request.body.raw.email);
});

B. pm.test('Status 201 and email match', () => {
pm.response.to.have.status(201);
const res = pm.response.json();
const req = JSON.parse(pm.request.body.raw);
pm.expect(res.email).to.eql(req.email);
});

C. pm.test('Status 201 and email match', () => {
pm.response.to.have.status(200);
const res = pm.response.json();
pm.expect(res.email).to.eql('[e-mail]');
});

D. pm.test('Status 201 and email match', () => {
pm.response.to.have.status(201);
pm.expect(pm.response.json().email).to.exist;
});

Solution

1. Step 1: Check status code assertion

   The test must check for status 201, which indicates resource creation.

2. Step 2: Compare response email with request email

   Since request body is raw JSON string, parse it with JSON.parse(pm.request.body.raw) to access email for comparison.

3. Step 3: Validate correct assertion

   pm.test('Status 201 and email match', () => { pm.response.to.have.status(201); const res = pm.response.json(); const req = JSON.parse(pm.request.body.raw); pm.expect(res.email).to.eql(req.email); }); correctly parses request body and compares res.email with req.email, ensuring they match.

4. Final Answer:

   pm.test('Status 201 and email match', () => { pm.response.to.have.status(201); const res = pm.response.json(); const req = JSON.parse(pm.request.body.raw); pm.expect(res.email).to.eql(req.email); }); -> Option B

5. Quick Check:

   Parse request body JSON before comparing fields [OK]

Hint: Parse request body JSON to compare fields in tests [OK]

Common Mistakes:

• Trying to access pm.request.body.raw.email directly without parsing
• Checking wrong status code like 200 instead of 201
• Only checking email exists without matching request value