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Mastering Unit Testing with Pytest

Testing Flask Applications

Explore how to write tests for Flask applications using pytest. Learn to create test client fixtures to simulate requests, test routes with GET and POST methods, handle dynamic URLs, and use mocking to isolate dependencies in unit tests. This lesson helps you ensure your Flask endpoints function correctly and your application remains robust.

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Flask test client fixture

In pytest, we can define fixtures to set up and tear down resources needed for the tests. In the case of Flask applications, we can create a fixture for the Flask test client, which allows us to make requests to the application endpoints during testing. Here’s an example of how to define a Flask test client fixture using pytest:

import pytest

from app import create_app



@pytest.fixture

def client():

    app = create_app()

    app.config['TESTING'] = True



    with app.test_client() as client:

        yield client
Flask test client

In the above example, we create a fixture named client using the pytest.fixture decorator. Inside the fixture function, we create an instance of the Flask application using the create_app() function from the application code. We then set the TESTING configuration flag to True to enable testing mode for the application.

Using the with statement, we create a ...