public void Sum_Method()
        {
            Assert.Throws <ArgumentNullException>(() => IYandexMoneyDonateFormWidgetExtensions.Sum(null, 0));

            new YandexMoneyDonateFormWidget().Do(widget =>
            {
                Assert.True(ReferenceEquals(widget.Sum(1.0), widget));
                Assert.Equal((decimal)1.0, widget.Sum());
            });
        }
        public void Text_Method()
        {
            Assert.Throws <ArgumentNullException>(() => IYandexMoneyDonateFormWidgetExtensions.Text(null, YandexMoneyDonateFormText.Donate));

            new YandexMoneyDonateFormWidget().Do(widget =>
            {
                Assert.True(ReferenceEquals(widget.Text(YandexMoneyDonateFormText.Donate), widget));
                Assert.Equal(1, widget.Text());
            });
            new YandexMoneyDonateFormWidget().Do(widget => Assert.Equal(2, widget.Text(YandexMoneyDonateFormText.Give).Text()));
            new YandexMoneyDonateFormWidget().Do(widget => Assert.Equal(3, widget.Text(YandexMoneyDonateFormText.Transfer).Text()));
            new YandexMoneyDonateFormWidget().Do(widget => Assert.Equal(4, widget.Text(YandexMoneyDonateFormText.Send).Text()));
            new YandexMoneyDonateFormWidget().Do(widget => Assert.Equal(5, widget.Text(YandexMoneyDonateFormText.Support).Text()));
        }