[Python] How to handle E2E API Request in Backend correctly?

I have set up an api backend using FastAPI. Backend testing has been done already. But I don't know how to test the frontend correctly which is usign the api. Because I want at least one test that is performed via a real API request. The only problem is that my backend uses a database, and I haven't found a sensible way to replace this database connection with a fake database connection so that it doesn't accidentally remain active in production due to some error.

Currently I use Jest but since I haven't taken any tests yet, you can also recommend others to me.

My frontend function to test

export default async function createTodoAPI(name, description, accessToken) {
const response = await fetch(`${import.meta.env.VITE_API_URL}/todo/create`, {
method: "POST",
headers: {
"Content-Type": "application/json",
"Authorization": `Bearer ${accessToken}`
},
body: JSON.stringify({name: name, description: description})
});

if (!response.ok) {
data = await response.json();
throw new Error(data.detail || "Creation failed: An unexpected error is occurred.");
};
}



What I tried, but somehow feel uncomfortable using:

import os
import sys
import logging

logger = logging.getLogger(__name__)

TEST_MODE: bool = os.getenv("TEST_MODE", "false").lower() == "true"
PRODUCTION: bool = os.getenv("IS_PRODUCTION", "false").lower() == "true"

# Defines the database url
if TEST_MODE and PRODUCTION:
logger.error("\nTEST MODE COULD NOT BE ACTIVATED WHILE THE PRODUCTION IS ACTIVATED TOO.")
sys.exit(1)
elif TEST_MODE:
DB_URL = "sqlite+aiosqlite:///:memory:"
logger.warning("\n\nTEST MODE IS ACTIVATED: Using in-memory database.\n\n")
else:
DB_URL = os.getenv("DATABASE_URL")

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