input: Write a python function to fetch users data from a database and return it as a JSON response.
  assert get_users() == jsonify([
      {'user_id': 1, 'user_name': 'Alice', 'user_email': 'alice@example.com'},
      {'user_id': 2, 'user_name': 'Bob', 'user_email': 'bob@example.com'}
  ])
  assert get_users() == jsonify([
      {'user_id': 3, 'user_name': 'Charlie', 'user_email': 'charlie@example.com'},
      {'user_id': 4, 'user_name': 'David', 'user_email': 'david@example.com'}
  ])
output: from flask import jsonify
  import sqlite3
  
  def get_users():
      connection = sqlite3.connect('database.db')
      cursor = connection.cursor()
      
      cursor.execute("SELECT user_id, user_name, user_email FROM users")
      users = cursor.fetchall()
      
      users_list = [
          {'user_id': user[0], 'user_name': user[1], 'user_email': user[2]}
          for user in users
      ]
      
      connection.close()
      
      return jsonify(users_list)