Body validation before sending in Postman - Test Execution Trace

Test Overview

This test checks if the request body contains all required fields and valid data before sending the API request. It verifies that the body is correctly structured and prevents sending invalid data.

Test Code - Postman Test Script

Postman

pm.test("Request body has required fields and valid data", () => {
    const body = pm.request.body.raw ? JSON.parse(pm.request.body.raw) : {};
    pm.expect(body).to.have.property('username').that.is.a('string').and.is.not.empty;
    pm.expect(body).to.have.property('email').that.is.a('string').and.match(/^\S+@\S+\.\S+$/);
    pm.expect(body).to.have.property('age').that.is.a('number').and.is.above(0);
});

Execution Trace - 5 Steps

Step	Action	System State	Assertion	Result
1	Test script starts and parses the request body JSON	Postman request body is available as raw JSON string	Check if body is parsed without error	PASS
2	Check if 'username' field exists, is a string, and not empty	Parsed body object with fields	'username' property exists and is a non-empty string	PASS
3	Check if 'email' field exists, is a string, and matches email pattern	Parsed body object with fields	'email' property exists and matches email regex	PASS
4	Check if 'age' field exists, is a number, and greater than 0	Parsed body object with fields	'age' property exists and is a positive number	PASS
5	All validations passed, request body is valid	Request ready to be sent with valid body	All previous assertions passed	PASS

Failure Scenario

Failing Condition: Request body is missing required fields or fields have invalid data

Execution Trace Quiz - 3 Questions

What does the test check first in the request body?

A If the response status is 200

B If the 'age' field is zero or negative

C If the 'username' field exists and is a non-empty string

D If the request headers are set

Key Result

Validating the request body before sending helps catch errors early and prevents sending bad data to the server, improving test reliability and API stability.

Practice

1. What is the main reason to validate the request body in Postman before sending it?

easy

A. To automatically generate response data

B. To ensure the data format and required fields are correct

C. To speed up the request sending process

D. To change the HTTP method of the request

Solution

1. Step 1: Understand the purpose of body validation

   Validating the request body helps catch errors like missing fields or wrong data types before sending.

2. Step 2: Identify the correct reason

   Ensuring data format and required fields are correct prevents server errors and improves test reliability.

3. Final Answer:

   To ensure the data format and required fields are correct -> Option B

4. Quick Check:

   Body validation = correct data format [OK]

Hint: Validate body to avoid sending bad data [OK]

Common Mistakes:

• Thinking validation speeds up sending
• Confusing validation with response generation
• Assuming validation changes HTTP method

2. Which Postman script snippet correctly checks if the raw request body contains a JSON field named username before sending?

easy

A. pm.expect(pm.response.body).to.have.property('username');

B. pm.request.body.raw.includes('username');

C. pm.expect(pm.request.body.raw).to.include('username');

D. pm.request.body.json().has('username');

Solution

1. Step 1: Identify correct method to check raw body content

   pm.request.body.raw returns the raw string body; using pm.expect(...).to.include('username') checks if 'username' text exists.

2. Step 2: Eliminate incorrect options

   pm.request.body.raw.includes('username'); returns boolean but no assertion; pm.expect(pm.response.body).to.have.property('username'); checks response, not request; pm.request.body.json().has('username'); uses invalid method.

3. Final Answer:

   pm.expect(pm.request.body.raw).to.include('username'); -> Option C

4. Quick Check:

   Use pm.expect with raw body to check text [OK]

Hint: Use pm.expect with raw body string to check fields [OK]

Common Mistakes:

• Checking response instead of request body
• Using non-existent methods on pm.request.body
• Not using pm.expect for assertions

3. Given this Postman pre-request script snippet:

const body = JSON.parse(pm.request.body.raw);
pm.expect(body.age).to.be.a('number');

What will happen if the request body is {"age": "twenty"}?

medium

A. The test will fail because age is a string, not a number

B. The test will pass because 'twenty' is a valid value

C. The script will throw a syntax error

D. The test will be skipped automatically

Solution

1. Step 1: Parse the request body and check type

   The script parses the JSON body and asserts that body.age is a number.

2. Step 2: Analyze the given body value

   Since age is the string "twenty", the assertion to be.a('number') fails.

3. Final Answer:

   The test will fail because age is a string, not a number -> Option A

4. Quick Check:

   Type check fails if data type mismatches [OK]

Hint: Check data types carefully in JSON body [OK]

Common Mistakes:

• Assuming string 'twenty' counts as number
• Expecting syntax error on valid JSON
• Thinking test skips on failure

4. You wrote this Postman pre-request test to check if the request body has a non-empty email field:

const body = JSON.parse(pm.request.body.raw);
pm.expect(body.email).to.not.be.empty;

But the test always passes even when email is missing. What is the likely problem?

medium

A. The raw body is not accessible in pre-request scripts

B. pm.expect cannot check empty strings

C. JSON.parse fails silently on missing fields

D. The test does not check if email exists before checking emptiness

Solution

1. Step 1: Understand the test logic

   The test checks if body.email is not empty, but if email is undefined, the assertion does not fail as expected.

2. Step 2: Identify missing existence check

   Without checking if email exists, the test passes because undefined is not considered empty string.

3. Final Answer:

   The test does not check if email exists before checking emptiness -> Option D

4. Quick Check:

   Check existence before emptiness to avoid false passes [OK]

Hint: Check field exists before checking empty [OK]

Common Mistakes:

• Assuming empty check covers missing fields
• Believing JSON.parse fails silently
• Thinking raw body is unavailable in pre-request

5. You want to prevent sending a request if the JSON body misses the required field id or if id is not a positive integer. Which Postman pre-request script correctly validates this before sending?

hard

A. const body = JSON.parse(pm.request.body.raw);
if (!body.id || typeof body.id !== 'number' || body.id <= 0) {
throw new Error('Invalid id');
}

B. const body = JSON.parse(pm.request.body.raw);
pm.expect(body.id).to.be.a('number').and.to.be.above(0);

C. const body = pm.request.body.raw;
pm.expect(body).to.include('id');

D. const body = JSON.parse(pm.request.body.raw);
if (body.id === undefined) {
console.log('Missing id');
}

Solution

1. Step 1: Check for existence and type with condition

   const body = JSON.parse(pm.request.body.raw); if (!body.id || typeof body.id !== 'number' || body.id <= 0) { throw new Error('Invalid id'); } parses the body and uses an if statement to check if id is missing, not a number, or not positive.

2. Step 2: Prevent sending by throwing error

   Throwing an error in pre-request script stops the request from sending, enforcing validation.

3. Final Answer:

   const body = JSON.parse(pm.request.body.raw); if (!body.id || typeof body.id !== 'number' || body.id <= 0) { throw new Error('Invalid id'); } -> Option A

4. Quick Check:

   Throw error to block invalid body before sending [OK]

Hint: Throw error in pre-request to block bad body [OK]

Common Mistakes:

• Using pm.expect without blocking request
• Only logging missing fields without stopping
• Checking raw string instead of parsed JSON