public void ContainLastItemOfFirstInputArray(NonEmptyList <object> list1, List <object> list2) =>
 list1.Append(list2).ListRef(list1.Length - 1)
 .Should().Be(list1.ListRef(list1.Length - 1));
 public void HaveSameFirstItemAsFirstInputArray(NonEmptyList <object> list1, List <object> list2) =>
 list1.Append(list2).ListRef(0)
 .Should().Be(list1.ListRef(0));