Added assertion to list integration tests

src/Hydrogen.NUnit/AssertEx.cs

@@ -34,6 +34,11 @@ public static void ListIntegrationTest<T>(
 		expected ??= new List<T>();
 		itemComparer ??= EqualityComparer<T>.Default;
 
+		// Test 0: Adding via indexing operator fails
+		var val = randomItemGenerator(RNG, 1).Single();
+		Assert.That(() => expected[0] = val, Throws.Exception);
+		Assert.That(() => list[0] = val, Throws.Exception);
+
 		// Test 1: Add nothing
 		expected.AddRangeSequentially(Enumerable.Empty<T>());
 		list.AddRange(Enumerable.Empty<T>());
@@ -239,6 +244,11 @@ public static void BufferIntegrationTest(
 		expected ??= new BufferAdapter(new List<byte>());
 		var itemComparer = ByteArrayEqualityComparer.Instance;
 
+		// Test 0: Adding via indexing operator fails
+		byte val = 23;
+		Assert.That(() => expected[0] = val, Throws.Exception);
+		Assert.That(() => buffer[0] = val, Throws.Exception);
+
 		// Test 1: Add nothing
 		expected.AddRange(Tools.Spans.Empty<byte>());
 		buffer.AddRange(Tools.Spans.Empty<byte>());

src/Hydrogen/Collections/Paged/PagedListBase.cs

@@ -375,15 +375,22 @@ protected void CheckLoaded() {
 	}
 
 	protected override void CheckIndex(long index, bool allowAtEnd = false) {
-		Guard.Ensure(InternalPages.Count > 0, "No pages");
+		if (allowAtEnd && index == 0)
+			return;
+
+		if (InternalPages.Count == 0)
+			throw new InvalidOperationException("No pages");
+
 		var startIX = InternalPages[0].StartIndex;
 		var lastIX = InternalPages[InternalPages.Count - 1].EndIndex;
 		var collectionCount = lastIX - startIX + 1;
 		Guard.CheckIndex(index, startIX, collectionCount, allowAtEnd);
 	}
 
 	protected override void CheckRange(long index, long count, bool rightAligned = false) {
-		Guard.Ensure(InternalPages.Count > 0, "No pages");
+		if (InternalPages.Count == 0)
+			throw new InvalidOperationException("No pages");
+
 		var startIX = InternalPages[0].StartIndex;
 		var lastIX = InternalPages[InternalPages.Count - 1].EndIndex;
 		var collectionCount = lastIX - startIX + 1;