API client testing in PyTest - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is API client testing?

API client testing checks if the code that talks to an API works correctly. It ensures the client sends requests and handles responses as expected.

beginner

Why do we mock API responses in client testing?

We mock API responses to test the client without calling the real API. This makes tests faster, reliable, and independent of the API server.

intermediate

What pytest feature helps to mock API calls?

The pytest feature called 'monkeypatch' or libraries like 'requests-mock' help replace real API calls with fake responses during tests.

intermediate

How do you check if an API client handles errors correctly?

Write tests that simulate error responses from the API and assert the client reacts properly, like raising exceptions or returning error messages.

intermediate

What is a good practice for API client test assertions?

Assert both the status code and the content of the response. Also, check that the client sends correct request data and headers.

What is the main goal of API client testing?

A To test the API server's performance

B To check the database schema

C To verify the client correctly communicates with the API

D To design the API endpoints

API client testing focuses on the client code that sends requests and processes responses from the API.

Which pytest tool helps replace real API calls with fake ones?

A assert

B fixture

C parametrize

D monkeypatch

monkeypatch allows you to replace parts of your code, like API calls, with mocks during tests.

Why should API client tests mock API responses?

A To increase test execution time

B To avoid network delays and make tests reliable

C To test the real API server

D To skip testing error cases

Mocking avoids real network calls, making tests faster and stable.

What should you assert in API client tests?

A Response status code and content

B Only the response time

C Only the request URL

D The API server logs

Checking both status code and content ensures the client handles responses correctly.

How can you test API client error handling?

A Simulate error responses and check client reactions

B Ignore error cases in tests

C Only test successful responses

D Test the API server instead

Simulating errors helps verify the client handles failures properly.

Explain how you would write a pytest test to check an API client method that fetches user data.

Think about replacing the real API call with a fake response and then verifying the client processes it correctly.

Describe why mocking is important in API client testing and how it improves test quality.

Consider what happens if tests depend on a real API server.

Practice

1. What is the main purpose of API client testing in pytest?

easy

A. To verify that the code correctly communicates with the API

B. To check the user interface layout

C. To test database schema changes

D. To measure application performance speed

Solution

1. Step 1: Understand API client testing goal

   API client testing ensures the code sends requests and receives responses correctly from an API.

2. Step 2: Compare options with API client testing focus

   Only To verify that the code correctly communicates with the API relates to verifying communication with the API, others focus on unrelated areas.

3. Final Answer:

   To verify that the code correctly communicates with the API -> Option A

4. Quick Check:

   API client testing = verify API communication [OK]

Hint: API client testing checks API communication correctness [OK]

Common Mistakes:

• Confusing API testing with UI testing
• Thinking it tests database directly
• Mixing performance testing with API client testing

2. Which pytest code snippet correctly asserts that an API response status code is 200?

easy

A. assert response.statusCode == 200

B. assert response.status == 200

C. assert response.code == 200

D. assert response.status_code == 200

Solution

1. Step 1: Identify correct attribute for status code in response

   In most Python HTTP clients, the status code is accessed via response.status_code.

2. Step 2: Verify assertion syntax

   The assertion assert response.status_code == 200 is syntactically correct and checks the status code properly.

3. Final Answer:

   assert response.status_code == 200 -> Option D

4. Quick Check:

   Correct attribute is status_code [OK]

Hint: Use response.status_code to check HTTP status [OK]

Common Mistakes:

• Using incorrect attribute names like status or code
• Missing assert keyword
• Using camelCase instead of snake_case

3. Given the pytest test below, what will be the output if the API returns JSON {'success': true}?

def test_api_response(client):
    response = client.get('/status')
    data = response.json()
    assert data['success'] is True

medium

A. Test fails due to assertion error

B. Test fails due to KeyError

C. Test passes because 'success' is True

D. Test raises a syntax error

Solution

1. Step 1: Analyze the API response and JSON parsing

   The API returns JSON with key 'success' set to true, which maps to Python True after parsing.

2. Step 2: Check the assertion logic

   The assertion checks if data['success'] is True, which matches the parsed value, so it passes.

3. Final Answer:

   Test passes because 'success' is True -> Option C

4. Quick Check:

   JSON true = Python True, assertion passes [OK]

Hint: True in JSON becomes True in Python, assertion passes [OK]

Common Mistakes:

• Confusing JSON true with string 'true'
• Expecting KeyError when key exists
• Misreading assertion logic

4. Identify the error in this pytest API test code:

def test_get_user(client):
    response = client.get('/user/1')
    assert response.status_code = 200
    assert response.json()['id'] == 1

medium

A. Using single equals '=' instead of double '==' in assertion

B. Missing parentheses in response.json call

C. Incorrect endpoint URL format

D. No error, code is correct

Solution

1. Step 1: Check assertion syntax

   The line assert response.status_code = 200 uses single '=' which is assignment, not comparison.

2. Step 2: Confirm correct assertion operator

   Assertions require '==' to compare values, so it should be assert response.status_code == 200.

3. Final Answer:

   Using single equals '=' instead of double '==' in assertion -> Option A

4. Quick Check:

   Use '==' for comparison in assert [OK]

Hint: Use '==' in assert, not '=' [OK]

Common Mistakes:

• Confusing assignment '=' with comparison '=='
• Forgetting parentheses in method calls
• Assuming no syntax error in assert

5. You want to test an API client method that sends a POST request with JSON data and expects a 201 status code. Which pytest test code correctly performs this check?

hard

A. def test_create_item(client):
response = client.post('/items', data={'name': 'book'})
assert response.status_code == 201

B. def test_create_item(client):
response = client.post('/items', json={'name': 'book'})
assert response.status_code == 201

C. def test_create_item(client):
response = client.post('/items', json='name=book')
assert response.status_code == 201

D. def test_create_item(client):
response = client.post('/items', json={'name': 'book'})
assert response.status == 201

Solution

1. Step 1: Identify correct way to send JSON data in POST request

   Using json={'name': 'book'} sends JSON properly; data= sends form data, which is incorrect here.

2. Step 2: Verify correct status code assertion

   Use response.status_code == 201 to check for created resource status; response.status is invalid.

3. Final Answer:

   def test_create_item(client): response = client.post('/items', json={'name': 'book'}) assert response.status_code == 201 -> Option B

4. Quick Check:

   Use json= for JSON, assert status_code == 201 [OK]

Hint: Use json= dict and assert status_code == 201 [OK]

Common Mistakes:

• Using data= instead of json= for JSON payload
• Passing JSON as string instead of dict
• Using response.status instead of response.status_code