[tryton] Inherit wizard class to add new button and duplicated btn

[Raimon Esteve]

Hie,

I have a module add new class wizard:

class TestClass(Wizard):
    __name__ = 'test.class'
    start = StateTransition()
    picking = StateView('test.class.view',
       ......
    tasktodo = StateTransition()
    result = StateView('test.class.result',
        'module.test_class_result', [
            Button('Done', 'end', 'tryton-ok'),
            ])

I have three modules inherit TestClass to do more features.

One module, add new btn in result view.

    @classmethod
    def __setup__(cls):
        super(TestClass, cls).__setup__()
        # add new button: Save Photo
        cls.result.buttons.insert(0,
            Button('Save Photo', 'photo', 'tryton-go-next', True))

When I installed three modules inherit TestClass , I detect this new
button (Save Photo), are duplicated (three modules = three buttons =
three registration class).

The reason is because each module registre class but I can't check if
new button are in cls.result.buttons to insert or not.

I solved with add all modules in extra_depends (module add new btn).

Other way to fix it?

Thanks