public void StateUndo()
{
State o = new State(null);
Assert.Empty(o.Move(1, 2, 1, 4));
Assert.Null(o.At(o.Live, 1, 2));
Assert.NotNull(o.At(o.Live, 1, 4));
Assert.False(o.At(o.Live, 1, 4).Inert);
Assert.Single(o.History);
o.Undo(o.LastNote());
Assert.Null(o.At(o.Live, 1, 4));
Assert.NotNull(o.At(o.Live, 1, 2));
Assert.True(o.At(o.Live, 1, 2).Inert);
Assert.Empty(o.History);
Assert.Empty(o.Move(1, 2, 1, 4));
Assert.Single(o.History);
}
