public void TestFalseOwnership()
{
// This test tries to make sure a WList doesn't get confused about what
// blocks it owns. It's possible for a WList to share a partially-mutable
// block that contains mutable items with another WList, but only one
// WList owns the items.
// Case 1: two WLists point to the same block but only one owns it:
//
// block 0
// owned by A
// |____3| block 1
// |____2| unowned
// A,B--->|Imm_1|--->|Imm_1|
// |____0| |____0|
//
// (The location of "Imm" in each block denotes the highest immutable
// item; this diagram shows there are two immutable items in each
// block)
WList <int> A = new WList <int>();
A.Resize(4);
for (int i = 0; i < 4; i++)
{
A[i] = i;
}
WList <int> B = A.Clone();
// B can't add to the second block because it's not the owner, so a
// third block is created when we Add(1).
B.Add(4);
A.Add(-4);
ExpectList(A, 0, 1, 2, 3, -4);
ExpectList(B, 0, 1, 2, 3, 4);
Assert.AreEqual(2, A.BlockChainLength);
Assert.AreEqual(3, B.BlockChainLength);
// Case 2: two WLists point to different blocks but they share a common
// tail, where one list owns part of the tail and the other does not:
//
// block 0
// owned by B
// |____8|
// |____7|
// |____6|
// |____5| block 1
// |____4| owned by A
// |____3| A |____3| block 2
// |____2| | |____2| unowned
// |____1|---+---->|Imm_1|---->|Imm_1|
// B--->|____0| |____0| |____0|
// mutable
//
// Actually the previous test puts us in just this state.
//
// I can't think of a test that uses the public interface to detect bugs
// in this case. The most important thing is that B._block.PriorIsOwned
// returns false.
Assert.That(B.IsOwner && !B.Block.PriorIsOwned);
Assert.That(A.IsOwner);
Assert.That(B.Block.Prior.ToVList() == A.WithoutLast(1));
}