Why testing validates contracts in Rest API - Challenge Your Understanding

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output when the API returns unexpected data?

Consider a REST API client that expects a JSON response with a status field set to success. The client tests the response to validate the contract.

What will be the output of the following code if the API returns {"status": "error", "message": "Invalid request"}?

Rest API

response = {"status": "error", "message": "Invalid request"}
if response.get("status") == "success":
    print("Contract validated: success")
else:
    print("Contract violation detected")

A Contract violation detected

B Contract validated: success

C KeyError exception

D No output

💡 Hint

Check the value of the status key in the response dictionary.

The code checks if the status key equals success. Since the API returned error, the else branch runs, printing "Contract violation detected".

🧠 Conceptual

intermediate

Why is testing important for API contracts?

Which of the following best explains why testing validates API contracts?

A Testing guarantees the API will never have bugs.

B Testing improves the API server's hardware performance.

C Testing ensures the API implementation matches the agreed request and response formats.

D Testing replaces the need for documentation.

💡 Hint

Think about what a contract means in API communication.

API contracts define how clients and servers communicate. Testing checks that the API behaves as promised, matching the contract's request and response formats.

🔧 Debug

advanced

Identify the error in this API contract test

The following test checks if the API response contains a data field with a list. What error will this code produce if the API returns {"data": null}?

Rest API

response = {"data": None}
if isinstance(response["data"], list):
    print("Valid data list")
else:
    print("Invalid data format")

A Invalid data format

B KeyError exception

C Valid data list

D TypeError exception

💡 Hint

Check the type of response["data"] when it is None.

The code checks if response["data"] is a list. Since it is None, the else branch runs, printing "Invalid data format". No exception occurs.

📝 Syntax

advanced

Which option causes a syntax error in this API test code?

Which of the following code snippets will cause a syntax error when testing an API response?

A if 'status' in response: print('OK')

B if response.get('status') == 'success': print('OK')

C if response.get('status') != 'error': print('OK')

D if response['status'] = 'success': print('OK')

💡 Hint

Look for the assignment operator used inside the if condition.

Option D uses = (assignment) instead of == (comparison) inside the if condition, causing a syntax error.

🚀 Application

expert

How many contract violations are detected in this batch test?

Given the following list of API responses, how many violate the contract that requires status to be success?

responses = [
  {"status": "success", "data": [1,2]},
  {"status": "error", "message": "fail"},
  {"status": "success", "data": []},
  {"status": "pending"}
]

Rest API

responses = [
  {"status": "success", "data": [1,2]},
  {"status": "error", "message": "fail"},
  {"status": "success", "data": []},
  {"status": "pending"}
]
violations = 0
for r in responses:
    if r.get("status") != "success":
        violations += 1
print(violations)

A 1

B 2

C 3

D 4

💡 Hint

Count how many responses have a status not equal to success.

Two responses have status values other than success: "error" and "pending". So, violations = 2.