Create a RoutedEventArgs subclass (e.g. CanExecuteRoutedEventArgs) for unit testing purposes.

CreateRoutedEventArgs.cs

        protected static T CreateRoutedEventArgs<T>() {
            var fakeCommand = Substitute.For<ICommand>();
            var nonPublicInstance = BindingFlags.NonPublic | BindingFlags.Instance;
            var ev = (RoutedEvent) Activator.CreateInstance(
                type: typeof(RoutedEvent),
                bindingAttr: nonPublicInstance,
                binder: null,
                args: new object[4] {null, null, null, null },
                culture: null);
            var args = (T) Activator.CreateInstance(
                type: typeof(T),
                bindingAttr: nonPublicInstance,
                binder: null,
                args: new object[2] { fakeCommand, null },
                culture: null);
            typeof(RoutedEventArgs)
                .GetField("_routedEvent", nonPublicInstance)
                .SetValue(args, ev);
            return args;
        }