Contract testing in Rest API - Mini Project: Build & Apply

Contract Testing for a REST API

📖 Scenario: You are working on a simple REST API that provides information about books in a library. To make sure the API works as expected for other developers who use it, you will write contract tests. These tests check that the API responses match the agreed format and data types.

🎯 Goal: Build a contract test that verifies the API response for the /books endpoint matches the expected structure and data types.

📋 What You'll Learn

Create a sample API response data structure

Define the expected contract for the API response

Write a test that compares the actual response to the contract

Print the test result indicating if the contract is met

💡 Why This Matters

🌍 Real World

Contract testing helps ensure that APIs deliver data in the format and types that clients expect, preventing bugs and misunderstandings.

💼 Career

Many software development roles require writing or understanding API contract tests to maintain reliable and stable services.

1

Create sample API response data

Create a variable called api_response that holds a list of dictionaries. Each dictionary represents a book with these exact keys and values: {'id': 1, 'title': '1984', 'author': 'George Orwell'} and {'id': 2, 'title': 'To Kill a Mockingbird', 'author': 'Harper Lee'}.

Rest API

# Create the variable api_response with the exact list of book dictionaries
# Your code here

Need a hint?

Use a list with two dictionaries exactly as shown.

2

Define the expected contract

Create a variable called expected_contract that holds a dictionary with keys id, title, and author. The values should be the expected data types: int for id and str for title and author.

Rest API

api_response = [
    {'id': 1, 'title': '1984', 'author': 'George Orwell'},
    {'id': 2, 'title': 'To Kill a Mockingbird', 'author': 'Harper Lee'}
]
# Define expected_contract with keys and their expected types
# Your code here

Need a hint?

Use a dictionary with keys matching the book keys and values as the Python types.

3

Write the contract test logic

Write a function called check_contract that takes response and contract as parameters. It should return True if every item in response has all keys in contract with values of the correct type. Otherwise, return False. Use a for loop with variables item and check each key and type.

Rest API

api_response = [
    {'id': 1, 'title': '1984', 'author': 'George Orwell'},
    {'id': 2, 'title': 'To Kill a Mockingbird', 'author': 'Harper Lee'}
]

expected_contract = {
    'id': int,
    'title': str,
    'author': str
}

# Define check_contract function to verify response matches contract
# Your code here

Need a hint?

Use nested loops to check each key and type in each item.

4

Print the contract test result

Use print to display the result of calling check_contract with api_response and expected_contract. The output should be True if the contract is met.

Rest API

api_response = [
    {'id': 1, 'title': '1984', 'author': 'George Orwell'},
    {'id': 2, 'title': 'To Kill a Mockingbird', 'author': 'Harper Lee'}
]

expected_contract = {
    'id': int,
    'title': str,
    'author': str
}

def check_contract(response, contract):
    for item in response:
        for key, expected_type in contract.items():
            if key not in item or not isinstance(item[key], expected_type):
                return False
    return True

# Print the result of check_contract with api_response and expected_contract
# Your code here

Need a hint?

Call the function and print its result.