Mocking external services in Flask - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Flask testing client.

Flask

from flask import Flask
from flask.testing import [1]

app = Flask(__name__)

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

ATestClient

BClient

CTestRequest

DFlaskClient

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'TestClient' which is not the correct Flask test client class.

Using 'Client' which is too generic and not from flask.testing.

The correct import for Flask's test client is FlaskClient. It allows you to simulate requests to your Flask app during tests.

2fill in blank

medium

Complete the code to patch the external API call using unittest.mock.

Flask

from unittest.mock import patch

@patch('[1]')
def test_api_call(mock_get):
    pass

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

Arequests.get

Bapp.get

Cflask.get

Dexternal.get

Attempts:

3 left

💡 Hint

Common Mistakes

Patching 'flask.get' which does not exist.

Patching 'app.get' which is unrelated to HTTP calls.

To mock an external HTTP GET request, you patch requests.get because requests is the library used to make HTTP calls.

3fill in blank

hard

Fix the error in the mock setup to return a JSON response.

Flask

mock_get.return_value.[1] = lambda: {'status': 'ok'}

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

Ajson_data

Bjson

Cjson.return_value()

Djson.return_value

Attempts:

3 left

💡 Hint

Common Mistakes

Mocking 'json' as a dict instead of a callable method.

Using 'json.return_value' without calling it as a function.

The requests.get method returns a response object whose json() method returns the JSON data. So you must mock json as a lambda returning the dict.

4fill in blank

hard

Fill both blanks to create a mock response with status code 200 and JSON data.

Flask

mock_response = MagicMock()
mock_response.[1] = 200
mock_response.[2].return_value = {'message': 'success'}

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

Astatus_code

Bjson

Ccontent

Dtext

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'content' or 'text' for JSON data instead of mocking 'json' method.

Setting 'status' instead of 'status_code'.

The HTTP status code is set with status_code. The JSON data is returned by the json() method, so we mock its return_value.

5fill in blank

hard

Fill all three blanks to patch 'requests.get', create a mock response, and assert the call was made.

Flask

with patch('[1]') as mock_get:
    mock_get.return_value.[2] = 200
    response = requests.get('http://example.com')
    mock_get.[3]('http://example.com')

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

Arequests.get

Bstatus_code

Cassert_called_with

Djson

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'assert_called_once' instead of 'assert_called_with' which checks arguments.

Setting 'status' instead of 'status_code'.

You patch requests.get to mock the HTTP call. The mock response's status_code is set to 200. Finally, you assert the mock was called with the expected URL using assert_called_with.

Practice

1. What is the main reason to mock external services in Flask testing?

easy

A. To change the Flask app configuration permanently

B. To speed up the Flask server in production

C. To add more routes to the Flask app

D. To avoid making real network calls during tests

Solution

1. Step 1: Understand the purpose of mocking

   Mocking replaces real external calls with fake ones to avoid delays and failures during tests.

2. Step 2: Identify the benefit in Flask testing

   This avoids real network calls, making tests faster and more reliable.

3. Final Answer:

   To avoid making real network calls during tests -> Option D

4. Quick Check:

   Mocking = Avoid real network calls [OK]

Hint: Mock to skip real network calls in tests [OK]

Common Mistakes:

• Thinking mocking speeds up production
• Confusing mocking with adding routes
• Believing mocking changes app config permanently

2. Which of the following is the correct way to patch an external function requests.get in a Flask test using unittest.mock?

easy

A. with patch('requests.get') as mock_get:

B. with patch(requests.get) as mock_get:

C. with patch('requests->get') as mock_get:

D. with patch('requests_get') as mock_get:

Solution

1. Step 1: Understand patch syntax

   Patch requires the full path as a string, e.g., 'requests.get'.

2. Step 2: Identify correct string format

   with patch('requests.get') as mock_get: uses the correct string 'requests.get'. Others use invalid syntax or missing quotes.

3. Final Answer:

   with patch('requests.get') as mock_get: -> Option A

4. Quick Check:

   Patch needs string path = with patch('requests.get') as mock_get: [OK]

Hint: Patch uses string path like 'module.function' [OK]

Common Mistakes:

• Passing function object instead of string
• Using wrong string format with arrows
• Missing quotes around patch target

3. Given this Flask test code snippet, what will be printed?

from unittest.mock import patch
import requests

def fetch_data():
    response = requests.get('http://example.com')
    return response.status_code

with patch('requests.get') as mock_get:
    mock_get.return_value.status_code = 404
    print(fetch_data())

medium

A. None

B. 200

C. 404

D. Raises an error

Solution

1. Step 1: Understand patch effect on requests.get

   The patch replaces requests.get with a mock whose return_value.status_code is set to 404.

2. Step 2: Trace fetch_data call inside patch

   fetch_data calls requests.get, which returns the mock with status_code 404, so fetch_data returns 404.

3. Final Answer:

   404 -> Option C

4. Quick Check:

   Mocked status_code = 404 [OK]

Hint: Mock return_value sets fake response attributes [OK]

Common Mistakes:

• Expecting real HTTP 200 response
• Confusing mock object with None
• Thinking patch causes error

4. What is wrong with this Flask test code that tries to mock requests.post?

from unittest.mock import patch
import requests

def send_data():
    response = requests.post('http://example.com', data={'key': 'value'})
    return response.ok

with patch('requests.post') as mock_post:
    mock_post.ok = True
    print(send_data())

medium

A. mock_post.ok should be set on return_value, not mock_post

B. patch target should be 'requests.get' not 'requests.post'

C. send_data should use requests.get instead of post

D. mock_post.ok is correct and code works fine

Solution

1. Step 1: Identify mock object usage

   mock_post is the mock for requests.post function, its return_value simulates the response object.

2. Step 2: Correct attribute assignment

   Setting mock_post.ok sets attribute on the function mock, not the response. It should be mock_post.return_value.ok = True.

3. Final Answer:

   mock_post.ok should be set on return_value, not mock_post -> Option A

4. Quick Check:

   Mock response attributes go on return_value [OK]

Hint: Set mock response attributes on return_value [OK]

Common Mistakes:

• Setting attributes on mock function instead of return_value
• Confusing post with get method
• Assuming code works without fixing mock

5. You want to test a Flask route that calls an external API and returns JSON data. Which approach correctly mocks the external API call and returns a custom JSON response {"success": true} during the test?

hard

A. Use patch on the Flask route function and return {"success": true} directly

B. Use patch on the external call, set return_value.json.return_value = {"success": true}

C. Call the real external API and check if it returns {"success": true}

D. Mock the Flask app config to include {"success": true}

Solution

1. Step 1: Identify what to mock

   The external API call (e.g., requests.get) should be mocked to avoid real network calls.

2. Step 2: Set mock return JSON data

   Set the mock's return_value.json.return_value to the desired JSON dict to simulate API response.

3. Final Answer:

   Use patch on the external call, set return_value.json.return_value = {"success": true} -> Option B

4. Quick Check:

   Mock external call's json() method = Use patch on the external call, set return_value.json.return_value = {"success": true} [OK]

Hint: Mock return_value.json.return_value for JSON responses [OK]

Common Mistakes:

• Mocking Flask route instead of external call
• Calling real API in tests
• Changing app config instead of mocking