Why isn't Django unit test seeing a raised exception? - django

Question

I'm trying to test a static method in one of my models but the test is not seeing an exception that's being raised and I don't understand why.
Here's the model and static method:
# models.py
class List(models.Model):
owner = models.ForeignKey(User)
type = models.ForeignKey('ListType', help_text=_('Type of list'))
name = models.CharField(_('list'), max_length=128, help_text=_('Name of list'))
class ListType(models.Model):
type = models.CharField(_('type'), max_length=16)
#staticmethod
def read_list(list_id, list_name, owner, list_type):
try:
return List.objects.get(pk=list_id, name=list_name, owner=owner, type=list_type)
except List.DoesNotExist:
return None
Here's the test:
# tests.py
from django.test import TestCase
from .factories import *
from .models import List, ListType
class TestFuncs(TestCase):
def test_read_list_exc(self):
with self.assertRaises(List.DoesNotExist):
uf = UserFactory()
lt = ListType.objects.get(type='Member')
lf = ListFactory(owner=uf, type=lt, name='foo')
# I've created one list but its name isn't 'bar'
list = List.read_list(999, 'bar', uf, lt)
If I set a debugging breakpoint in the read_list method and run the test, I do see the exception being raised:
# set_trace output:
(<class 'list.models.DoesNotExist'>, DoesNotExist('List matching query does not exist.',))
# test output:
...
File "...."
list = List.read_list(999, 'bar', uf, lt)
AssertionError: DoesNotExist not raised
I've read other questions here about how to detect this type of exception and I thought I was doing it right. Just for fun, I changed the test to the following but that didn't resolve the problem:
...
with self.assertRaises(list.models.DoesNotExist):
...
Can anyone see what I'm doing wrong?

Answer 1

In the static method you catch the exception and return None.
You could either change the test to use assertIsNone.
l = List.read_list(999, 'bar', uf, lt) # don't use list as a variable
self.assertIsNone(l)
Or if you really do want the method to raise the exception, then remove the try..except.
#staticmethod
def read_list(list_id, list_name, owner, list_type):
return List.objects.get(pk=list_id, name=list_name, owner=owner, type=list_type)

Answer 2

You already handled DoesNotExist exception inside read_list so it's not thrown to the test case.
To throw exception you can use raise operator:
#staticmethod
def read_list(list_id, list_name, owner, list_type):
try:
return List.objects.get(pk=list_id, name=list_name, owner=owner, type=list_type)
except List.DoesNotExist as e:
some actions to handle exception, for example logging
...
raise e