How do I validate status codes and JSON payloads in API tests?

To validate status codes and JSON payloads in API tests, you typically check two things:

1. The HTTP response status
2. The response body structure and values

1) Validate status codes

Check that the API returns the expected HTTP code, such as:

• 200 OK for successful GET/PUT requests
• 201 Created for successful POST requests
• 204 No Content for successful deletes
• 400 Bad Request for validation errors
• 401 Unauthorized / 403 Forbidden for auth issues
• 404 Not Found for missing resources
• 500 Internal Server Error for unexpected failures

Example

• If you call GET /users/1, expect 200
• If you call POST /users with valid data, expect 201
• If you call DELETE /users/1, expect 204

2) Validate JSON payloads

Verify that the response body:

• is valid JSON
• has the expected fields
• has correct data types
• contains expected values
• does not contain unexpected/malformed data

Example checks

For a response like:

{
  "id": 1,
  "name": "Alice",
  "email": "alice@example.com"
}

You might validate:

• id is present and is a number
• name equals "Alice"
• email is present and matches an email format

3) Common assertions to use

Depending on your test tool/framework, assertions usually look like:

• Status code
  • assert response.status_code == 200
• JSON key exists
  • assert "id" in response.json()
• Exact value
  • assert response.json()["name"] == "Alice"
• Type check
  • assert isinstance(response.json()["id"], int)
• Array length
  • assert len(response.json()) > 0

4) Example in Python (requests + pytest)

import requests

def test_get_user():
    response = requests.get("https://api.example.com/users/1")

    assert response.status_code == 200

    data = response.json()
    assert data["id"] == 1
    assert data["name"] == "Alice"
    assert "email" in data

5) Example in JavaScript (fetch + Jest`)

test('get user', async () => {
  const response = await fetch('https://api.example.com/users/1');
  expect(response.status).toBe(200);

  const data = await response.json();
  expect(data.id).toBe(1);
  expect(data.name).toBe('Alice');
  expect(data.email).toBeDefined();
});

6) Good practices

• Validate both happy path and error cases
• Check schema/structure, not only exact values
• Assert critical fields only; avoid overly brittle tests
• Use JSON schema validation for larger payloads
• Separate tests for:
  • status code
  • response body
  • headers
  • error handling

7) Schema validation example

If your API has a known contract, use JSON Schema to ensure the payload matches expected structure and types.

Example checks:

• required fields exist
• types are correct
• no extra fields if your contract forbids them

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If you want, I can also show you how to do this in Postman, RestAssured, pytest, or Cypress.