app.py

from flask import Flask


# create and initialize a new Flask app
app = Flask(__name__)


@app.route("/")
def hello():
    return "Hello, World!"


if __name__ == "__main__":
    app.run()

app_test.py

from project.app import app


def test_index():
    tester = app.test_client()
    response = tester.get("/", content_type="html/text")

    assert response.status_code == 200
    assert response.data == b"Hello, World!"

TDD on Python

I'm using version 3.12 on virtual env with wsl2
- make sure to activate the virutal env `source venv/bin/activate`
- I'm using flask as framework `pip install flask==3.0.0` then continue with `pip install pytest==7.4.2`
- make skeleton project like this:
├── project
│   ├── __init__.py
│   ├── app.py
└── tests
    ├── __init__.py
    └── app_test.py
- open tests/app_test.py and add the following code (see file app_test.py)
- begin the test `python -m pytest`, it goes fail with `ImportError: cannot import name 'app' from 'project.app`
- open project/app.py and add following code (see app.py)
- run the app with `FLASK_APP=project/app.py python -m flask run -p 5001` then navigate your browser to `http://localhost:5001`
- Return to the terminal. Kill the server with Ctrl+C. Run the test again `python -m pytest`