old_contents: from traits.testing.unittest_tools import unittest
  
  from traits.api import Float, HasTraits, Int, List
  
  
  class Foo(HasTraits):
      x = Float
  
      x_changes = List
      y_changes = List
  
      def _x_changed(self, new):
          self.x_changes.append(new)
  
      def _y_changed(self, new):
          self.y_changes.append(new)
  
  
  class TestDynamicTraitDefinition(unittest.TestCase):
      """ Test demonstrating special change events using the 'event' metadata.
      """
  
      def test_add_trait(self):
          foo = Foo(x=3)
          foo.add_trait('y', Int)
  
          self.assertTrue(hasattr(foo, 'y'))
          self.assertEqual(type(foo.y), int)
  
          foo.y = 4
          self.assertEqual(foo.y_changes, [4])
  
      def test_remove_trait(self):
          foo = Foo(x=3)
  
          # We can't remove a "statically" added trait (i.e., a trait defined
          # in the Foo class).
          result = foo.remove_trait('x')
          self.assertFalse(result)
  
          # We can remove dynamically added traits.
          foo.add_trait('y', Int)
          foo.y = 70
  
          result = foo.remove_trait('y')
          self.assertTrue(result)
  
          self.assertFalse(hasattr(foo, 'y'))
          foo.y = 10
          self.assertEqual(foo.y_changes, [70])
  
new_contents: from traits.testing.unittest_tools import unittest
  
  from traits.api import Float, HasTraits, Int, List
  
  
  class Foo(HasTraits):
      x = Float
  
      y_changes = List
  
      def _y_changed(self, new):
          self.y_changes.append(new)
  
  
  class TestDynamicTraitDefinition(unittest.TestCase):
      """ Test demonstrating special change events using the 'event' metadata.
      """
  
      def test_add_trait(self):
          foo = Foo(x=3)
          foo.add_trait('y', Int)
  
          self.assertTrue(hasattr(foo, 'y'))
          self.assertEqual(type(foo.y), int)
  
          foo.y = 4
          self.assertEqual(foo.y_changes, [4])
  
      def test_remove_trait(self):
          foo = Foo(x=3)
  
          # We can't remove a "statically" added trait (i.e., a trait defined
          # in the Foo class).
          result = foo.remove_trait('x')
          self.assertFalse(result)
  
          # We can remove dynamically added traits.
          foo.add_trait('y', Int)
          foo.y = 70
  
          result = foo.remove_trait('y')
          self.assertTrue(result)
  
          self.assertFalse(hasattr(foo, 'y'))
          foo.y = 10
          self.assertEqual(foo.y_changes, [70])
  
subject: Remove unused trait definitions in test.