Contract testing in Rest API - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a contract test that checks the response status code.

Rest API

def test_api_response():
    response = client.get('/api/data')
    assert response.status_code == [1]

Drag options to blanks, or click blank then click option'

A500

B404

C200

D302

Attempts:

3 left

💡 Hint

Common Mistakes

Using 404 which means Not Found

Using 500 which means Server Error

The expected status code for a successful API response is 200.

2fill in blank

medium

Complete the code to check that the response content type is JSON.

Rest API

def test_content_type():
    response = client.get('/api/data')
    assert response.headers['Content-Type'] == [1]

Drag options to blanks, or click blank then click option'

Atext/html

Bapplication/json

Ctext/plain

Dapplication/xml

Attempts:

3 left

💡 Hint

Common Mistakes

Using text/html which is for web pages

Using application/xml which is for XML data

The API should return data in JSON format, so the content type must be application/json.

3fill in blank

hard

Fix the error in the contract test that verifies the JSON response has a 'name' field.

Rest API

def test_response_has_name():
    response = client.get('/api/user')
    data = response.json()
    assert [1] in data

Drag options to blanks, or click blank then click option'

A'name'

B'username'

C'id'

D'email'

Attempts:

3 left

💡 Hint

Common Mistakes

Checking for 'username' instead of 'name'

Checking for 'email' which is not required

The contract requires the JSON response to include the 'name' field.

4fill in blank

hard

Fill both blanks to create a contract test that verifies the 'age' field is an integer and greater than 18.

Rest API

def test_age_field():
    response = client.get('/api/user')
    data = response.json()
    assert isinstance(data['age'], [1]) and data['age'] [2] 18

Drag options to blanks, or click blank then click option'

Aint

B>

C<

Dstr

Attempts:

3 left

💡 Hint

Common Mistakes

Using str instead of int

Using < instead of >

The 'age' field must be an integer and greater than 18 to meet the contract.

5fill in blank

hard

Fill all three blanks to write a contract test that filters users with 'active' status and checks their 'email' contains '@'.

Rest API

def test_active_users_email():
    response = client.get('/api/users')
    users = response.json()
    active_users = [user[1] user in users if user['status'] [2] 'active']
    assert all('[3]' in user['email'] for user in active_users)

Drag options to blanks, or click blank then click option'

A for

B==

C@

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of '==' for status check

Missing '@' in email check

Incorrect list comprehension syntax

The list comprehension uses for to iterate, == to check status, and '@' to verify emails.

Practice

1. What is the main purpose of contract testing in REST APIs?

easy

A. To check the API's user interface design

B. To test the speed of the API response

C. To ensure two systems agree on the data they exchange

D. To monitor server hardware performance

Solution

1. Step 1: Understand contract testing definition

   Contract testing checks if two systems agree on the data format and behavior during communication.

2. Step 2: Compare options to definition

   Only To ensure two systems agree on the data they exchange matches this purpose; others relate to speed, UI, or hardware, which are unrelated.

3. Final Answer:

   To ensure two systems agree on the data they exchange -> Option C

4. Quick Check:

   Contract testing = data agreement [OK]

Hint: Contract testing checks data agreement between systems [OK]

Common Mistakes:

• Confusing contract testing with performance testing
• Thinking contract testing checks UI or hardware
• Assuming contract testing is about security

2. Which of the following is the correct way to define a contract test for a REST API endpoint?

easy

A. Test the API's front-end layout on different browsers

B. Measure the time taken for the API to respond

C. Verify the API server's CPU usage during requests

D. Check if the API returns the expected status code and response body

Solution

1. Step 1: Identify contract test elements

   Contract tests verify the API response matches the agreed format, including status codes and body content.

2. Step 2: Match options to contract test definition

   Check if the API returns the expected status code and response body matches this exactly; others relate to performance, server metrics, or UI, which are not contract tests.

3. Final Answer:

   Check if the API returns the expected status code and response body -> Option D

4. Quick Check:

   Contract test = expected response check [OK]

Hint: Contract tests check expected status and response body [OK]

Common Mistakes:

• Confusing contract tests with performance or UI tests
• Ignoring response body content in contract tests
• Testing server hardware instead of API contract

3. Given this contract test snippet in JavaScript using Pact: <pre>provider.addInteraction({ state: 'user exists', uponReceiving: 'a request for user data', withRequest: { method: 'GET', path: '/user/123' }, willRespondWith: { status: 200, body: { id: 123, name: 'Alice' } } }); What will happen if the provider returns status 404 instead of 200 during the test?

medium

A. The test will pass because the body matches the contract

B. The test will fail because the status code doesn't match the contract

C. The test will ignore the status code and only check the path

D. The test will pass if the response time is fast enough

Solution

1. Step 1: Understand the contract test expectation

   The contract expects a 200 status code with a specific body when requesting '/user/123'.

2. Step 2: Analyze the provider's actual response

   The provider returns 404, which does not match the expected 200 status code.

3. Final Answer:

   The test will fail because the status code doesn't match the contract -> Option B

4. Quick Check:

   Status mismatch causes test failure [OK]

Hint: Mismatch in status code causes contract test failure [OK]

Common Mistakes:

• Assuming body match overrides status code mismatch
• Ignoring status code in contract tests
• Thinking response time affects contract test result

4. You wrote a contract test that expects a JSON response with a field email. The test fails because the provider returns emailAddress instead. What is the best way to fix this?

medium

A. Change the provider to return email as expected by the contract

B. Update the contract to expect emailAddress instead of email

C. Ignore the field mismatch and pass the test anyway

D. Remove the email field from the contract test

Solution

1. Step 1: Identify contract responsibility

   The contract defines the expected data format; the provider must follow it.

2. Step 2: Choose the correct fix

   Changing the provider to return email matches the contract, ensuring stable integration.

3. Final Answer:

   Change the provider to return email as expected by the contract -> Option A

4. Quick Check:

   Provider must match contract fields [OK]

Hint: Provider must match contract fields exactly [OK]

Common Mistakes:

• Ignoring field name mismatches
• Changing contract to fit provider without agreement
• Removing important fields from contract

5. You have two microservices: Service A (consumer) and Service B (provider). Service A expects Service B's API to return a list of products with fields id, name, and price. You want to write a contract test that allows price to be optional (sometimes missing). Which approach best achieves this?

hard

A. Define the contract so price is optional using a matcher that allows missing fields

B. Require price always in the contract and fail if missing

C. Remove price from the contract entirely

D. Ignore the contract and test only after deployment

Solution

1. Step 1: Understand optional fields in contract testing

   Contract tests can use matchers to allow fields to be optional or have flexible types.

2. Step 2: Choose the approach that supports optional price

   Defining price as optional with a matcher allows the provider to omit it without failing the test.

3. Final Answer:

   Define the contract so price is optional using a matcher that allows missing fields -> Option A

4. Quick Check:

   Use matchers for optional fields in contracts [OK]

Hint: Use matchers to allow optional fields in contract tests [OK]

Common Mistakes:

• Forcing optional fields to be always present
• Removing important fields from contract
• Skipping contract tests and testing only post-deployment