class EditProjectForm(ModelForm):
    def __init__(self, action, *args, **kwargs):
        super(EditProjectForm, self).__init__(*args, **kwargs)

        now = datetime.datetime.now()
        if action == 'edit':
            project_year = kwargs['project_year']
            self.fields['year'].choices = [(project_year, project_year)]
        else:
            self.fields['year'].choices = [(now.year, now.year), (now.year + 1, now.year + 1)]

    year = forms.TypedChoiceField(coerce=int)
    ...

form_params = {
    'project_year': datetime.datetime.now().year,
}
form = EditProjectForm('new', form_params)
self.assertTrue(form.is_valid())