Why Postman is essential for API testing - Test Execution Impact

Test Overview

This test checks if a simple GET request to a public API endpoint using Postman returns a successful response. It verifies that the API is reachable and responds with status code 200.

Test Code - Postman

Postman

GET https://jsonplaceholder.typicode.com/posts/1

// In Postman, send the GET request and verify the response status code is 200.

Execution Trace - 5 Steps

Step	Action	System State	Assertion	Result
1	Open Postman application	Postman interface is ready for creating requests	—	PASS
2	Create a new GET request to 'https://jsonplaceholder.typicode.com/posts/1'	Request tab shows the URL and GET method selected	—	PASS
3	Click the 'Send' button to execute the request	Postman sends the request to the API server	—	PASS
4	Receive response from API	Response tab shows status code 200 and JSON body with post data	Verify response status code is 200	PASS
5	Verify response body contains expected keys like 'userId', 'id', 'title', 'body'	Response JSON is displayed with expected keys	Check presence of keys in response JSON	PASS

Failure Scenario

Failing Condition: API endpoint is unreachable or returns error status code

Execution Trace Quiz - 3 Questions

What is the first step when testing an API with Postman?

A Check the database directly

B Open Postman and create a new request

C Write code to call the API

D Restart the API server

Key Result

Using Postman for API testing helps testers quickly send requests and verify responses without writing code, making API testing accessible and efficient.

Practice

1. Why is Postman considered essential for API testing?

easy

A. It replaces the need for any backend development.

B. It is only used for designing websites.

C. It allows easy and fast testing of APIs without coding.

D. It is a tool for creating mobile apps.

Solution

1. Step 1: Understand Postman's purpose

   Postman is designed to test APIs quickly and easily, especially without needing to write code.

2. Step 2: Compare options with Postman's features

   Options B, C, and D describe unrelated uses, while A correctly states Postman's role in API testing.

3. Final Answer:

   It allows easy and fast testing of APIs without coding. -> Option C

4. Quick Check:

   Postman simplifies API testing = A [OK]

Hint: Postman tests APIs fast without coding [OK]

Common Mistakes:

• Confusing Postman with web design tools
• Thinking Postman replaces backend coding
• Assuming Postman is for mobile app creation

2. Which of the following is the correct way to send a GET request in Postman?

easy

A. Select GET method and enter URL

B. Select POST method and enter URL

C. Select DELETE method and enter URL

D. Select PUT method and enter URL

Solution

1. Step 1: Identify the HTTP method for retrieving data

   GET is the standard HTTP method used to request data from a server.

2. Step 2: Match the method with Postman selection

   In Postman, to send a GET request, you must select GET and enter the URL.

3. Final Answer:

   Select GET method and enter URL -> Option A

4. Quick Check:

   GET method retrieves data = A [OK]

Hint: GET method is for fetching data [OK]

Common Mistakes:

• Choosing POST instead of GET for data retrieval
• Confusing DELETE or PUT with GET
• Not selecting any HTTP method

3. Consider this Postman test script snippet:

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

What will be the test result if the API response status is 404?

medium

A. Test will pass because 404 is a valid status

B. Test will fail because status is not 200

C. Test will error due to syntax mistake

D. Test will be skipped automatically

Solution

1. Step 1: Understand the test condition

   The test checks if the response status code equals 200.

2. Step 2: Compare actual status with expected

   The actual status is 404, which does not match 200, so the test fails.

3. Final Answer:

   Test will fail because status is not 200 -> Option B

4. Quick Check:

   Status 404 ≠ 200 means test fails = C [OK]

Hint: Test passes only if status matches expected [OK]

Common Mistakes:

• Assuming 404 is acceptable status for this test
• Thinking syntax error causes failure
• Believing test skips on mismatch

4. You wrote this Postman test:

pm.test("Response has userId", function () {
    pm.expect(pm.response.json().userId).to.exist;
});

But the test always fails. What is the most likely reason?

medium

A. The response JSON does not contain the key 'userId'.

B. The test syntax is incorrect and causes error.

C. Postman does not support JSON response testing.

D. The API endpoint URL is missing.

Solution

1. Step 1: Analyze the test code

   The test checks if the JSON response has a key named 'userId'.

2. Step 2: Identify why test fails

   If the test fails, it means 'userId' is missing in the response JSON, not a syntax error.

3. Final Answer:

   The response JSON does not contain the key 'userId'. -> Option A

4. Quick Check:

   Missing key in JSON causes test failure = B [OK]

Hint: Check if JSON key exists in response [OK]

Common Mistakes:

• Assuming syntax error causes failure
• Believing Postman can't test JSON
• Ignoring API endpoint correctness

5. You want to automate running multiple API tests and share results with your team. Which Postman feature helps achieve this?

hard

A. Using Postman only for API design, not testing.

B. Manually sending requests one by one and emailing screenshots.

C. Writing API tests only in external code editors without Postman.

D. Using Postman Collections with automated test scripts and sharing via Postman Cloud.

Solution

1. Step 1: Identify automation and sharing features in Postman

   Postman Collections allow grouping API requests with tests, which can be run automatically and shared via Postman Cloud.

2. Step 2: Compare options for automation and sharing

   Using Postman Collections with automated test scripts and sharing via Postman Cloud describes this feature correctly; others describe manual or unrelated approaches.

3. Final Answer:

   Using Postman Collections with automated test scripts and sharing via Postman Cloud. -> Option D

4. Quick Check:

   Collections + automation + sharing = D [OK]

Hint: Use Collections for automation and sharing [OK]

Common Mistakes:

• Thinking manual testing is automation
• Ignoring Postman's sharing features
• Confusing Postman with external editors only