how to write django test meant to fail?

If you're expecting Thing(name='1234') to raise an exception, there are two ways to deal with this.

One is to use Django's assertRaises (actually from unittest/unittest2):

def mytest(self):
    self.assertRaises(FooException, Thing, name='1234')

This fails unless Thing(name='1234') raises a FooException error. Another way is to catch the expected exception and raise one if it doesn't happen, like this:

def mytest(self):
    try:
        thing = Thing(name='1234')
        self.fail("your message here")
    except FooException:
        pass

Obviously, replace the FooException with the one you expect to get from creating the object with too long a string. ValidationError?

A third option (as of Python 2.7) is to use assertRaises as a context manager, which makes for cleaner, more readable code:

def mytest(self):
    with self.assertRaises(FooException):
        thing = Thing(name='1234')

Sadly, this doesn't allow for custom test failure messages, so document your tests well. See https://hg.python.org/cpython/file/2.7/Lib/unittest/case.py#l97 for more details.

I am currently using the expectedFailure decorator from unittest. That works as advertised: Fails when there is no error, passes when there is a failure.

I use expectedFailure to verify that my custom assert-routines actually work and not just rubberstamp everything OK.

import unittest
from django.test import TestCase

class EmojiTestCase(TestCase):

    @unittest.expectedFailure
    def testCustomAssert(self):
        self.assertHappyFace(':(') # must fail.

But prints a warning-message during testing. I use it with Django and Nose. Which others have seen, too.

/usr/lib64/python3.4/unittest/case.py:525: RuntimeWarning: TestResult has no addExpectedFailure method, reporting as passes RuntimeWarning)

I came here to find a better solution, but found none. So I at least wanted to tell others that come what I've been working with.

how to write django test meant to fail?

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