How to test the python backend of a flask application?

Question

I have a draft of a flask application with a html/javascript frontend and a python backend, to which the frontend communicates through the flask API.

I want to test the python backend using the API using python only (no javascript etc involved in the testing). I found this page with some suggestion but I guess something is missing.

I have tried the following test code in tests/test1.py:

from flask import Flask

app = Flask(__name__)

def test_1():
    """Example test"""
    response = app.test_client().get('/')
    print(response)

but the response returns a 404 error. I usually start the web server with flask run --host 0.0.0.0 using this server.py script:

import sys
import json
from flask import Flask, request, render_template

app = Flask(__name__)

from mf import gameplay

game = gameplay.Game()

@app.route('/')
def index():
    return render_template('mainmap.html')

@app.route('/api', methods=['POST'])
def api():
    data_json = request.data.decode()
    data = json.loads(data_json)
    return game(data_json)

if __name__ == '__main__':
    app.run('0.0.0.0', 5000, threaded=True)

I guess I am missing something to start the test?

I found some examples HERE and HERE that use something like

flask_app = create_app('flask_test.cfg')

but 1. flask does not have a method create_app and 2. what is the content of the config file (even not shown on the documentation of flask itself: HERE ...???)? I did not find one example...

Answer 1

You're creating a new application in your test module - meaning that you have no registered endpoints.

You'll need to import the app created in your server module.

from your_package.server import app

and use that as you're currently doing.

Ideally your server.py and your app.py are separate - meaning you have app.py with your app configuration and server.py imports the app required, and tests import the app required, so on and so forth.

Example:

application.py

import sys
import json
from flask import Flask, request, render_template

app = Flask(__name__)

from mf import gameplay

game = gameplay.Game()

@app.route('/')
def index():
    return render_template('mainmap.html')

@app.route('/api', methods=['POST'])
def api():
    data_json = request.data.decode()
    data = json.loads(data_json)
    return game(data_json)

server.py

from application import app
app.run('0.0.0.0', 5000, threaded=True)

test.py

from application import app

def test_1():
    """Example test"""
    with app.test_client() as client:
        response = client.get('/')
        print(response)

That should work!

Answer 2

Forget flask for these tests! You start the server as usual, and then in your test code you make request calls like

import json, requests
r = requests.post('http://192.168.1.28:5000/api', data=json.dumps(data))

with whatever data (defined as a python dict). The URL is as defined in your python flask start script (the http is important, and no not end the path with a slash ("/")), and api is the interface you also define in the python flask start script.

Now you can make tests with a single running instance of your flask server!