public void CharStream_CanRememberStates(string input, int savedIndex)
{
var cs = new CharStream(input);
for (int i = 0; i < savedIndex; i++)
cs.Read();
var expectedChar = cs.Peek().Value;
var rp = cs.CreateRestorePoint();
while (cs.Read() != null) ;
var end = cs.Read();
Assert.True(!end.HasValue);
rp();
var foundChar = cs.Peek();
Assert.True(foundChar.HasValue);
Assert.Equal(expectedChar, foundChar.Value);
}