django selenium测试关闭浏览器太早了

Question

我正在学习django这本书：用Python测试驱动开发 问题是我的功能测试得到随机结果 它有时会通过测试，而且大部分时间都没有 虽然它失败了，但错误提示是：
$('element').closest('some_top_element').find('another_bottom_element')。

我注意到在测试结束之前，浏览器总是过早关闭。但我不知道为什么以及如何解决它。

from django.contrib.staticfiles.testing import StaticLiveServerTestCase
from selenium import webdriver
from selenium.webdriver.common.keys import Keys


class NewVisitorTest(StaticLiveServerTestCase):
    def setUp(self):
        self.browser = webdriver.Firefox()
        self.browser.implicitly_wait(10)

    def tearDown(self):
        self.browser.quit()

    def check_for_row_in_list_table(self, row_text):
        table = self.browser.find_element_by_id('id_list_table')
        rows = table.find_elements_by_tag_name('tr')
        self.assertIn(row_text, [row.text for row in rows])

    def test_01_can_start_a_list_and_retrieve_it_later(self):
        # Edith has heard about a cool new online to-do app. She goes
        # to check out its homepage
        self.browser.get(self.live_server_url)
        self.browser.set_window_size(1024, 768)

        # She notices the input box is nicely centered
        inputbox = self.browser.find_element_by_id('id_new_item')
        self.assertAlmostEqual(
            inputbox.location['x'] + inputbox.size['width'] / 2,
            512,
            delta=5
        )
        # She notices the page title and header mention to-do lists
        self.assertIn('To-Do', self.browser.title)
        header_text = self.browser.find_element_by_tag_name('h1').text
        self.assertIn('To-Do', header_text)

        # She is invited to enter a to-do item straight away
        inputbox = self.browser.find_element_by_id('id_new_item')
        self.assertEqual(
            inputbox.get_attribute('placeholder'),
            'Enter a to-do item'
        )

        # She types "Buy peacock feathers" into a text box (Edith's hobby
        # is tying fly-fishing lures)
        inputbox.send_keys('Buy peacock feathers')

        # When she hits enter, the page updates, and now the page lists
        # "1: Buy peacock feathers" as an item in a to-do list
        inputbox.send_keys(Keys.ENTER)
        edith_list_url = self.browser.current_url
        self.assertRegex(edith_list_url, '/lists/.+')
        self.check_for_row_in_list_table('1: Buy peacock feathers')

        # There is still a text box inviting her to add another item. She
        # enters "Use peacock feathers to make a fly" (Edith is very methodical)

        inputbox = self.browser.find_element_by_id('id_new_item')
        inputbox.send_keys('Use peacock feathers to make a fly')
        inputbox.send_keys(Keys.ENTER)

        # The page updates again, and now shows both items on her list
        # self.check_for_row_in_list_table('2: Use peacock feathers to make a fly')
        # self.check_for_row_in_list_table('1: Buy peacock feathers')

        # Now a new user, Francis, comes along to the site.

        ## We use a new browser session to make sure that no information
        ## of Edith's is coming through from cookies etc #
        self.browser.quit()
        self.browser = webdriver.Firefox()

        # Francis visits the home page. There is no sign of Edith's
        # list
        self.browser.get(self.live_server_url)
        page_text = self.browser.find_element_by_tag_name('body').text
        self.assertNotIn('Buy peacock feathers', page_text)
        self.assertNotIn('make a fly', page_text)

        # Francis starts a new list by entering a new item. He
        # is less interesting than Edith...
        inputbox = self.browser.find_element_by_id('id_new_item')
        inputbox.send_keys('Buy milk')
        inputbox.send_keys(Keys.ENTER)

        # Francis gets his own unique URL
        francis_list_url = self.browser.current_url
        self.assertRegex(francis_list_url, '/lists/.+')
        self.assertNotEqual(francis_list_url, edith_list_url)

        # Again, there is no trace of Edith's list
        page_text = self.browser.find_element_by_tag_name('body').text
        self.assertNotIn('Buy peacock feathers', page_text)
        self.assertIn('Buy milk', page_text)

        # Satisfied, they both go back to sleep