Assert that two lists of objects are equal in django testing

Question

Is there a way to check that two lists of objects are equal in django tests.

lets say I have some model:

class Tag(models.Model):
    slug = models.SlugField(max_length=50, unique=True)
    def __unicode__(self):
        return self.slug

and I run this simple test:

def test_equal_list_fail(self):
    tag_list = []
    for tag in ['a', 'b', 'c']:
        tag_list.append(Tag.objects.create(slug=tag))

    tags = Tag.objects.all()

    self.assertEqual(tag_list, tags)

this fails with:

======================================================================
FAIL: test_equal_list_fail (userAccount.tests.ProfileTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "path/to/tests.py", line 155, in test_equal_list_fail
    self.assertEqual(tag_list, tags)
AssertionError: [<Tag: a>, <Tag: b>, <Tag: c>] != [<Tag: a>, <Tag: b>, <Tag: c>]

----------------------------------------------------------------------

this will work:

def test_equal_list_passes(self):
    tag_list = []
    for tag in ['a', 'b', 'c']:
        tag_list.append(Tag.objects.create(slug=tag))

    tags = Tag.objects.all()

    for tag_set in zip(tags, tag_list):
        self.assertEqual(*tag_set)

However, This fails:

def test_equal_list_fail(self):
    tag_list = []
    for tag in ['a', 'b', 'c']:
        tag_list.append(Tag.objects.create(slug=tag))

    tags = Tag.objects.all()

    for tag_set in zip(tags, tag_list):
        print "\n"
        print tag_set[0].slug + "'s pk is %s" % tag_set[0].pk
        print tag_set[1].slug + "'s pk is %s" % tag_set[1].pk
        print "\n"
        self.assertIs(*tag_set)

with:

Creating test database for alias 'default'...
.......

a's pk is 1
a's pk is 1

F.
======================================================================
FAIL: test_equal_list_fail (userAccount.tests.ProfileTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "path/to/tests.py", line 160, in test_equal_list_fail
    self.assertIs(*tag_set)
AssertionError: <Tag: a> is not <Tag: a>

Is this expected behavior?

Edit in response to comment
This type of comparison works:

class Obj:
    def __init__(self, x):
        self.x = x

>>> one = Obj(1)
>>> two = Obj(2)
>>> a = [one, two]
>>> b = [one, two]
>>> a == b
True

Why is the test failing for the other arrays?

Answer 1

To test two lists

use: assertSequenceEqual

Because, in this case, tags = Tag.objects.all() generates a django.db.models.query.QuerySet where as tag_list.append(...) creates a list.

Other options in different situations are:

• assertListEqual(a, b)
• assertTupleEqual(a, b)
• assertSetEqual(a, b)
• assertDictEqual(a, b)

Why <Tag: a> is not <Tag: a>

The tags are the same model, but they've been loaded into different places in memory

for tag_set in zip(tags, tag_list):
    print "\n"
    print tag_set[0].slug + "'s pk is %s" % tag_set[0].pk + ' id is: ' + id(tag_set[0])
    print tag_set[1].slug + "'s pk is %s" % tag_set[1].pk + ' id is: ' + id(tag_set[1])
    print "\n"
    self.assertIs(*tag_set)

returns

.......

a's pk is 1 id is: 4522000208
a's pk is 1 id is: 4522228112

F.

Therefore, is will retrun False

Answer 2

I think what you want to test is if the tags created have the same slugs as those in your test list.

For that, fetch only the slug as a list with values_list, and then compare that:

assertEqual(Tag.objects.values_list('slug', flat=True), ['a','b','c'])

I have to say, this isn't quite a useful test because you are checking django orm functionality, which has already been tested quite well.

Your tests should check for specifics of your own application.