LimitedSet does not perform as expected - tests fail

[caronc]

Checklist

• Celery Version v3.1.25
• [ X] I have verified that the issue exists against the master branch of Celery.

Steps to reproduce

Run unit tests

Expected behavior

That they'd pass 😉

Actual behavior

Why they all pass except the ones related to LimitedSet

The results appear to be the absolute invert of what is expected; have a look; here is the output:

__________________________________________________ test_LimitedSet.test_add ___________________________________________________

self = <celery.tests.utils.test_datastructures.test_LimitedSet testMethod=test_add>

    def test_add(self):
        if sys.platform == 'win32':
            raise SkipTest('Not working properly on Windows')
        s = LimitedSet(maxlen=2)
        s.add('foo')
        s.add('bar')
        for n in 'foo', 'bar':
            self.assertIn(n, s)
        s.add('baz')
        for n in 'bar', 'baz':
>           self.assertIn(n, s)
E           AssertionError: 'bar' not found in LimitedSet(2)

celery/tests/utils/test_datastructures.py:185: AssertionError
__________________________________________________ test_LimitedSet.test_iter __________________________________________________

self = <celery.tests.utils.test_datastructures.test_LimitedSet testMethod=test_iter>

    def test_iter(self):
        if sys.platform == 'win32':
            raise SkipTest('Not working on Windows')
        s = LimitedSet(maxlen=3)
        items = ['foo', 'bar', 'baz', 'xaz']
        for item in items:
            s.add(item)
        l = list(iter(s))
        for item in items[1:]:
>           self.assertIn(item, l)
E           AssertionError: 'bar' not found in ['baz', 'foo', 'xaz']

celery/tests/utils/test_datastructures.py:242: AssertionError
_________________________________________________ test_LimitedSet.test_update _________________________________________________

self = <celery.tests.utils.test_datastructures.test_LimitedSet testMethod=test_update>

    def test_update(self):
        s1 = LimitedSet(maxlen=2)
        s1.add('foo')
        s1.add('bar')
    
        s2 = LimitedSet(maxlen=2)
        s2.update(s1)
        self.assertItemsEqual(list(s2), ['foo', 'bar'])
    
        s2.update(['bla'])
>       self.assertItemsEqual(list(s2), ['bla', 'bar'])

celery/tests/utils/test_datastructures.py:280: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
celery/tests/case.py:367: in assertItemsEqual
    return self.assertSequenceEqual(expected, actual, msg=msg)
E   AssertionError: Sequences differ: ['bla', 'foo'] != ['bar', 'bla']
E   
E   First differing element 0:
E   bla
E   bar
E   
E   - ['bla', 'foo']
E   + ['bar', 'bla']

Just to give you more details on my environment (in case it's related):

• I'm using CentOS 7.x putting my on Python 2.7.5
• billiard v3.3.0.20
• kombu v3.0.37
• pyparsing v1.5.6
• pytest v3.0.6
• dateutil v2.2-1
• anyjson v0.3.3
• amqp v2.1.4
• pytz v2016.10
• uuid v1.30