public void TextNavigator_IsDigit_1()
        {
            const string  text      = "A1BC";
            TextNavigator navigator = new TextNavigator(text);

            Assert.IsFalse(navigator.IsDigit());
            navigator.ReadChar();
            Assert.IsTrue(navigator.IsDigit());
            navigator.ReadChar();
            Assert.IsFalse(navigator.IsDigit());
        }