public void ReturnCharsInCorrectOrder()
        {
            var text = "abc";
            var sut  = new TextWindowWithNull(text);

            Assert.Equal('a', sut.PeekChar());
            sut.ConsumeChar();
            Assert.Equal('b', sut.PeekChar());
            sut.ConsumeChar();
            Assert.Equal('c', sut.PeekChar());
            sut.ConsumeChar();
            Assert.Equal('\0', sut.PeekChar());
        }
        public void ReturnNullGivenEmptyText()
        {
            var sut = new TextWindowWithNull("");

            Assert.True(sut.PeekChar() == '\0');
        }