void NextNonWhiteChar_at_start()
{
var reader = new SourceStringReader(" \t \r abc");
var success = reader.AdvanceUntilNonWhite();
Assert.True(success);
Assert.Equal('a', reader.CurrentChar());
}
void NextNonWhiteChar_returns_false_when_no_more_nonwhite()
{
var reader = new SourceStringReader(" \t \r \n \r ");
Assert.False(reader.AdvanceUntilNonWhite());
}