input: Write a python function to access a database and retrieve all restaurant reviews.
  assert access_database(mock_db) == expected_results
  assert access_database(mock_db_empty) == []
  assert access_database(mock_db_with_one_review) == expected_single_review
output: def access_database(db_connection):
      query = "SELECT * FROM restaurant_reviews"
      cursor = db_connection.cursor()
      cursor.execute(query)
      results = cursor.fetchall()
      cursor.close()
      return results