在 Python unittest 中，有没有办法编写在断言失败时运行的代码？

Question

I'm using the Python unittest library to write some tests with Selenium. One of these tests involves going forward from one page to the next, checking an assertion, and then returning to the previous page as so:

def test_CheckNextPage(self):
     self.nextPageLink.click()
     self.assertEqual('The Next Page', self.driver.title)
     self.driver.back()

If in the event that the assertion fails, the self.driver.back() line is never reached and so all further tests are run on the wrong page, leading to them all being errors.

Is there any way to write a block of code to be run in the event of a failure after an assertion, so if it fails I can run some different code than if the assertion were to pass? (this block of course including the self.driver.back() line).

Answer 1

You're probably looking for the tearDown method. A generic example is below.

import unittest

class SimpleWidgetTestCase(unittest.TestCase):
    def setUp(self):
        self.widget = Widget('The widget')

    def runTest(self):
        # your test

    def tearDown(self):
        self.widget.dispose()
        self.widget = None

If setUp() succeeded, the tearDown() method will be run whether runTest() succeeded or not.

Look at the setUp and tearDown part of the documentation.

Answer 2

For this case, I fixed the issue by using a try/except to effectively create two different execution paths. One path for in the event the assertion fails, and another for when it passes.

def test_CheckNextPage(self):
     self.nextPageLink.click()
     try: self.assertEqual('The Next Page', self.driver.title)
     except: 
          self.driver.back()
          self.fail("Page title does not match expectation")

     self.driver.back()

In doing this, we get the full failure report from the assertion, and our manual failure message. This way we can ensure that self.driver.back() is called no matter what so that the rest of the tests will run correctly.