[FIXED] Why am I getting 404 when testing in pytest simple Flask app using create_app factory

Issue

I'm trying to make a small Flask app based on client-server architecture. I'm struggling with arranging app with pytest to make tests use prepared database. Here's project structure:

|   config.py
|   Pipfile
|                
+---client
+---mobile_app
+---server
|   |   database.py
|   |   server.py
|           
+---tests
|   |   test_database.py
|   |   test_server.py
|   |   __init__.py

Below content of server.py

    from flask import Flask
    from flask_restful import Api, Resource
    
    def create_app(config_obj):
        app = Flask(__name__)
        app.config.from_object(config_obj)
        return app
    
    app = create_app('config.DefaultConfig')
    api = Api(app)
    
    class Balance(Resource):
    
        @staticmethod
        def get(user_id):
            balance = 0 * user_id
            return {"balance": balance}
    
    api.add_resource(Balance, "/<int:user_id>/balance")
    
    if __name__ == "__main__":
        app.run(debug=True)

config.py:

class DefaultConfig:
    DEBUG = True
    TESTING = False
    PROPAGATE_EXCEPTIONS = None
    SECRET_KEY = 'mysecretkey'
    PERMANENT_SESSION_LIFETIME = '31 days, 0: 00:00'
    USE_X_SENDFILE = False
    SERVER_NAME = None
    APPLICATION_ROOT = '/'
    SESSION_COOKIE_NAME = 'session'
    SESSION_COOKIE_DOMAIN = None
    SESSION_COOKIE_PATH = None
    SESSION_COOKIE_HTTPONLY = True
    SESSION_COOKIE_SECURE = False
    SESSION_COOKIE_SAMESITE = None
    SESSION_REFRESH_EACH_REQUEST = True
    MAX_CONTENT_LENGTH = None
    SEND_FILE_MAX_AGE_DEFAULT = None
    TRAP_BAD_REQUEST_ERRORS = None
    TRAP_HTTP_EXCEPTIONS = False
    EXPLAIN_TEMPLATE_LOADING = False
    PREFERRED_URL_SCHEME = 'http'
    TEMPLATES_AUTO_RELOAD = None
    MAX_COOKIE_SIZE = 4093


class TestingConfig:
    DEBUG = True
    TESTING = True
    PROPAGATE_EXCEPTIONS = True
    SECRET_KEY = 'mysecretkey'
    PERMANENT_SESSION_LIFETIME = '31 days, 0: 00:00'
    USE_X_SENDFILE = False
    SERVER_NAME = None
    APPLICATION_ROOT = '/'
    SESSION_COOKIE_NAME = 'session'
    SESSION_COOKIE_DOMAIN = None
    SESSION_COOKIE_PATH = None
    SESSION_COOKIE_HTTPONLY = True
    SESSION_COOKIE_SECURE = False
    SESSION_COOKIE_SAMESITE = None
    SESSION_REFRESH_EACH_REQUEST = True
    MAX_CONTENT_LENGTH = None
    SEND_FILE_MAX_AGE_DEFAULT = None
    TRAP_BAD_REQUEST_ERRORS = None
    TRAP_HTTP_EXCEPTIONS = False
    EXPLAIN_TEMPLATE_LOADING = False
    PREFERRED_URL_SCHEME = 'http'
    TEMPLATES_AUTO_RELOAD = None
    MAX_COOKIE_SIZE = 4093

and last but not least - test_server.py

import pytest
from server.server import create_app, app


@pytest.fixture()
def client_not_working():
    client = create_app('config.TestingConfig')
    with client.test_client() as testing_client:
        # with client.app_context():
        #     yield testing_client
        yield testing_client

@pytest.fixture()
def client_working():

    yield app.test_client()

fixture = client_not_working

def test_get_balance(fixture):
    response = fixture.get('/1/balance')
    assert response.status_code == 200
    assert response.headers['Content-Type'] == 'application/json'
    assert b'balance' in response.data
    assert response.json["balance"] == 0

If I set fixture as client_working test is passed. But when I set fixture as client_not_working which I want to use to customize configuration, i get Assertion Error:

    tests\test_server.py:19 (test_get_balance)
    404 != 200
    
    Expected :200
    Actual   :404
    <Click to see difference>
    
    fixture = <FlaskClient <Flask 'server.server'>>
    
        def test_get_balance(fixture):
            response = fixture.get('/1/balance')
    >       assert response.status_code == 200
    E       assert 404 == 200
    E        +  where 404 = <WrapperTestResponse streamed [404 NOT FOUND]>.status_code
    
    tests\test_server.py:22: AssertionError

What am I doing wrong?

Solution

I figured out some obvious solution. The API resource wasn't built around object that was created by create_app factory, but it was built around app instance, that was functioning only in server.py itself.

I put those line, responsible for building Api around app into the factory and it works now.

server.py:

from flask import Flask
from flask_restful import Api, Resource

class Balance(Resource):

    @staticmethod
    def get(user_id):
        balance = 0 * user_id
        return {"balance": balance}


def create_app(config_obj):
    app = Flask(__name__)
    app.config.from_object(config_obj)

    api = Api(app)
    api.add_resource(Balance, "/<int:user_id>/balance")
    return app


app = create_app('config.DefaultConfig')


if __name__ == "__main__":
    # na środowisku produkcyjnym wyłączyć tryb debug!
    # najlepiej stworzyć main.py uwzględniający rozruch serwera
    app.run(debug=True)

Answered By - kubablo