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#  Copyright (c) 2013, Enthought, Inc.
#  All rights reserved.
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#  license included in /LICENSE.txt and may be redistributed only
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""" Test cases for weakref (WeakRef) traits. """

import contextlib
import gc

from traits.testing.unittest_tools import unittest, UnittestTools

from ..trait_types import Str, WeakRef
from ..has_traits import HasTraits


class Eggs(HasTraits):
    name = Str


class Spam(HasTraits):
    eggs = WeakRef(Eggs)


@contextlib.contextmanager
def restore_gc_state():
    """Ensure that gc state is restored on exit of the with statement."""
    originally_enabled = gc.isenabled()
    try:
        yield
    finally:
        if originally_enabled:
            gc.enable()
        else:
            gc.disable()


class TestWeakRef(UnittestTools, unittest.TestCase):
    """ Test cases for weakref (WeakRef) traits. """

    def test_set_and_get(self):
        eggs = Eggs(name='platypus')
        spam = Spam()
        self.assertIsNone(spam.eggs)
        spam.eggs = eggs
        self.assertIs(spam.eggs, eggs)
        del eggs
        self.assertIsNone(spam.eggs)

    def test_target_freed_notification(self):
        eggs = Eggs(name='duck')
        spam = Spam(eggs=eggs)

        # Removal of the last reference to 'eggs' should trigger notification.
        with self.assertTraitChanges(spam, 'eggs'):
            del eggs

    def test_weakref_trait_doesnt_leak_cycles(self):
        eggs = Eggs(name='ostrich')
        with restore_gc_state():
            gc.disable()
            gc.collect()
            spam = Spam(eggs=eggs)
            del spam
            self.assertEqual(gc.collect(), 0)
