如果 setUpClass 抛出异常，如何使 python 单元测试失败

Question

I am having little trouble using the python setUpClass.

For example consider the following case

class MyTest(unittest.case.TestCase):

    @classmethod
    def setUpClass(cls):
        print "Test setup"
        try:
            1/0
        except:
            raise

    @classmethod
    def tearDownClass(cls):
        print "Test teardown"

A couple of questions

1. Is the above code the right way to handle test setUpClass exceptions (by raising it so that the python unittest can take care of it), there are fail(), skip() methods, but those can only be used by test instances and not the test classes.

2. When there is a setUpClass exception, how can we ensure that tearDownClass runs (unittest doesn't run it, should we manualy call it).

Answer 1

You can call tearDownClass on an exception as Jeff points it out, but you may also implements the __del__(cls) method :

import unittest

class MyTest(unittest.case.TestCase):

    @classmethod
    def setUpClass(cls):
        print "Test setup"
        try:
            1/0
        except:
            raise

    @classmethod
    def __del__(cls):
        print "Test teardown"

    def test_hello(cls):
        print "Hello"

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

Will have the following output :

Test setup
E
======================================================================
ERROR: setUpClass (__main__.MyTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "my_test.py", line 8, in setUpClass
    1/0
ZeroDivisionError: integer division or modulo by zero

----------------------------------------------------------------------
Ran 0 tests in 0.000s

FAILED (errors=1)
Test teardown

Note : you should be aware that the __del__ method will be called at the end of the program execution, which is maybe not what you want if you have a more than one test class.

Hope it helps

Answer 2

The best option would be is to add handler for the except which calls tearDownClass and re-raise exception.

@classmethod
def setUpClass(cls):
    try:
        super(MyTest, cls).setUpClass()
        # setup routine...
    except Exception:  # pylint: disable = W0703
        super(MyTest, cls).tearDownClass()
        raise

Answer 3

import contextlib

class MyTestCase(unitest.TestCase):

    @classmethod
    def setUpClass(cls):
        with contextlib.ExitStack() as stack:
            # ensure teardown is called if error occurs
            stack.callback(cls.tearDownClass)

            # Do the things here!

            # remove callback at the end if no error found
            stack.pop_all()

Answer 4

use tearDownModule. It should be called after setUpClass runs.