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# (C) Copyright 2005-2023 Enthought, Inc., Austin, TX
# All rights reserved.
#
# This software is provided without warranty under the terms of the BSD
# license included in LICENSE.txt and may be redistributed only under
# the conditions described in the aforementioned license. The license
# is also available online at http://www.enthought.com/licenses/BSD.txt
#
# Thanks for using Enthought open source!
import unittest
from traits.api import Constant, HasTraits, TraitError
class TestConstantTrait(unittest.TestCase):
def test_initial_value(self):
class TestClass(HasTraits):
c_atr = Constant(5)
self.assertEqual(TestClass().c_atr, 5)
def test_mutable_initial_value(self):
class TestClass(HasTraits):
c_atr_1 = Constant([1, 2, 3, 4, 5])
c_atr_2 = Constant({"a": 1, "b": 2})
obj = TestClass()
self.assertEqual(obj.c_atr_1, [1, 2, 3, 4, 5])
self.assertEqual(obj.c_atr_2, {"a": 1, "b": 2})
def test_assign_fails(self):
class TestClass(HasTraits):
c_atr = Constant(5)
with self.assertRaises(TraitError):
TestClass(c_atr=5)
with self.assertRaises(TraitError):
del TestClass().c_atr
def test_mutate_succeeds(self):
class TestClass(HasTraits):
c_atr_1 = Constant([1, 2, 3, 4, 5])
c_atr_2 = Constant({"a": 1, "b": 2})
obj = TestClass()
obj.c_atr_1.append(6)
obj.c_atr_2["c"] = 3
self.assertEqual(obj.c_atr_1, [1, 2, 3, 4, 5, 6])
self.assertEqual(obj.c_atr_2, {"a": 1, "b": 2, "c": 3})
def test_mutate_affects_all_instances(self):
# Mutable values are allowed for the 'Constant' trait because it's
# impractical to do otherwise - many things are mutable but not
# intended to be mutated, and there's no practical way to test for
# "not-intended-to-be-mutated". Nevertheless, actually mutating the
# value for 'Constant' is inadvisable in practice, despite the
# existence of this test.
class TestClass(HasTraits):
c_atr = Constant([1, 2, 3, 4, 5])
obj1 = TestClass()
obj2 = TestClass()
# Mutate obj2; check that obj1 is affected.
obj2.c_atr.append(6)
self.assertEqual(obj1.c_atr, [1, 2, 3, 4, 5, 6])
# Check directly that both refer to the same object.
self.assertIs(obj1.c_atr, obj2.c_atr)
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