Why testing validates contracts in Rest API - See It in Action

Why Testing Validates Contracts in REST APIs

📖 Scenario: You are working on a simple REST API that provides user information. The API contract specifies that when you request a user by ID, you get a JSON response with id, name, and email. Testing helps ensure the API follows this contract exactly.

🎯 Goal: Build a simple test that checks if the API response matches the expected contract. This shows how testing validates that the API behaves as promised.

📋 What You'll Learn

Create a sample API response dictionary with user data

Define the expected contract keys in a list

Write a test that checks if all contract keys exist in the response

Print the test result as 'Contract Validated' or 'Contract Failed'

💡 Why This Matters

🌍 Real World

APIs must follow contracts so different programs can work together without errors. Testing these contracts prevents bugs and confusion.

💼 Career

Many software jobs require writing tests to verify APIs meet their contracts, ensuring reliable communication between services.

1

Create the sample API response data

Create a dictionary called api_response with these exact entries: 'id': 101, 'name': 'Alice', 'email': '[e-mail]', and 'age': 30.

Rest API

# Your code here

Need a hint?

Use curly braces {} to create a dictionary with the exact keys and values.

2

Define the expected contract keys

Create a list called contract_keys with these exact strings: 'id', 'name', and 'email'.

Rest API

api_response = {'id': 101, 'name': 'Alice', 'email': '[e-mail]', 'age': 30}
# Your code here

Need a hint?

Use square brackets [] to create a list with the exact strings.

3

Write the test to check the contract

Write a for loop using key to iterate over contract_keys. Inside the loop, check if key is not in api_response. If missing, set a variable valid to False and break the loop. Before the loop, set valid to True.

Rest API

api_response = {'id': 101, 'name': 'Alice', 'email': '[e-mail]', 'age': 30}
contract_keys = ['id', 'name', 'email']
# Your code here

Need a hint?

Start with valid = True. Use a for loop and if to check keys. Use break to stop if a key is missing.

4

Print the test result

Write a print statement that prints 'Contract Validated' if valid is True, otherwise prints 'Contract Failed'.

Rest API

api_response = {'id': 101, 'name': 'Alice', 'email': '[e-mail]', 'age': 30}
contract_keys = ['id', 'name', 'email']
valid = True
for key in contract_keys:
    if key not in api_response:
        valid = False
        break
# Your code here

Need a hint?

Use a single print with a conditional expression to show the result.