在Python中编写Selenium Unittests的正确方法？

我有以下场景:

Load Page A
Check if Element_A exists in Page A
Click Button_A
On Clicking Button_A, Page B is loaded
Check if Element_B exists in Page B and Click Button_B
and so on...

我写了这样的代码:

import unittest
from selenium import webdriver
from selenium.webdriver.common.keys import Keys

class MyWebsiteTest(unittest.TestCase):

    def setUp(self):
        self.driver = webdriver.Firefox()

    def test_element_a_in_page_a(self):
        driver = self.driver
        driver.get(PAGE_A)
        element = driver.get_element_by_id("element_a")
        self.assertIsNotNone(element,"Oops.")

    def load_page_b_if_previous_function_is_true(self):
        #WHAT DO I DO HERE?
        #I Need to run this function given test_element_a_in_page_a succeeds.

    def tearDown(self):
        self.driver.close()

if __name__ == "__main__":
    unittest.main()

我该怎么做呢？我怎么写load_page_b_if_element_a_in_page_a？

如果我在一个函数中编写整个测试流程,那么我可以轻松实现它,但是如何分离关注点呢？如何在不多次打开firefox的情况下将任务划分为不同的功能？