private List <XY> GetWallLocations(FacilityLayer layer)
 {
     return(layer.Where(IsFloor)
            .SelectMany(y => layer.GetNeighbors(y.Location).Where(x => !IsFloor(x)))
            .Select(z => z.Location)
            .Distinct().ToList());
 }
 private void AssertWallCountIs(int expected)
 {
     Assert.AreEqual(expected, _layer.Where(IsWall).Count());
 }