input: Write a python function to fetch user profile from a database using user_id.
  assert get_user_profile('1') == {'username': 'johndoe', 'name': 'John Doe', 'email': 'johndoe@example.com'}
  assert get_user_profile('2') == {'username': 'janedoe', 'name': 'Jane Doe', 'email': 'janedoe@example.com'}
  assert get_user_profile('3') == {'username': 'samsmith', 'name': 'Sam Smith', 'email': 'samsmith@example.com'}
output: def get_user_profile(user_id):
      # Mock database as a dictionary
      database = {
          '1': {'username': 'johndoe', 'name': 'John Doe', 'email': 'johndoe@example.com'},
          '2': {'username': 'janedoe', 'name': 'Jane Doe', 'email': 'janedoe@example.com'},
          '3': {'username': 'samsmith', 'name': 'Sam Smith', 'email': 'samsmith@example.com'},
      }
      return database.get(user_id)