Reproduce ArgumentOutOfRangeException when entity doesn't match pat…

…ches (#87)

ChronoJsonDiffPatch/ChronoJsonDiffPatchTests/ListPatchingTests.cs

@@ -0,0 +1,130 @@
+using System.Text.Json.Serialization;
+using ChronoJsonDiffPatch;
+using FluentAssertions;
+
+namespace ChronoJsonDiffPatchTests;
+
+public class ListPatchingTests
+{
+    internal record ListItem
+    {
+        [JsonPropertyName("value")] public string Value { get; set; }
+    }
+
+    internal record EntityWithList
+    {
+        [JsonPropertyName("myList")] public List<ListItem> MyList { get; set; }
+    }
+
+
+    [Fact]
+    public void Test_List_Patching_Generally_Works_With_Add_And_Reverse()
+    {
+        var chain = new TimeRangePatchChain<EntityWithList>();
+        var initialEntity = new EntityWithList
+        {
+            MyList = new List<ListItem>
+            {
+                new() { Value = "Foo" },
+                new() { Value = "Bar" }
+            }
+        };
+        {
+            var updatedEntity1 = new EntityWithList
+            {
+                MyList = new List<ListItem>
+                {
+                    new() { Value = "fOO" },
+                    new() { Value = "bAR" }
+                }
+            };
+            var keyDate1 = new DateTimeOffset(2024, 1, 1, 0, 0, 0, TimeSpan.Zero);
+            chain.Add(initialEntity, updatedEntity1, keyDate1);
+
+            chain.Count.Should().Be(2); // [-infinity, keyDate1); [keyDate1, +infinity)
+            ReverseAndRevert(chain, initialEntity);
+        }
+
+        {
+            var updatedEntity2 = new EntityWithList
+            {
+                MyList = new List<ListItem>
+                {
+                    new() { Value = "fOO" },
+                    new() { Value = "bAR" },
+                    new() { Value = "bAZ" }
+                }
+            };
+            var keyDate2 = new DateTimeOffset(2025, 1, 1, 0, 0, 0, TimeSpan.Zero);
+            chain.Add(initialEntity, updatedEntity2, keyDate2);
+
+            chain.Count.Should().Be(3); // [-infinity, keyDate1); [keyDate1, keyDate2); [keyDate2, +infinity)
+            ReverseAndRevert(chain, initialEntity);
+        }
+
+        {
+            var updatedEntity3 = new EntityWithList
+            {
+                MyList = new List<ListItem>
+                {
+                    new() { Value = "Not so foo anymore" },
+                    new() { Value = "bAR" },
+                    new() { Value = "bAZ" }
+                }
+            };
+            var keyDate3 = new DateTimeOffset(2025, 1, 1, 0, 0, 0, TimeSpan.Zero);
+            chain.Add(initialEntity, updatedEntity3, keyDate3);
+
+            ReverseAndRevert(chain, initialEntity);
+        }
+    }
+
+    /// <summary>
+    /// In <see cref="Test_List_Patching_Generally_Works_With_Add_And_Reverse"/> we showed that adding and removing list entries is generally well-supported by this library.
+    /// In this test, we show, than when users run into an <see cref="ArgumentOutOfRangeException"/>, this is probably due to initial entities not matching the expected state (corrupted).
+    /// </summary>
+    [Fact]
+    public void Reproduce_ArgumentOutOfRangeException()
+    {
+        var chain = new TimeRangePatchChain<EntityWithList>();
+        var initialEntity = new EntityWithList
+        {
+            MyList = new List<ListItem>
+            {
+                new() { Value = "My First Value" },
+            }
+        };
+        var keyDate1 = new DateTimeOffset(2024, 1, 1, 0, 0, 0, TimeSpan.Zero);
+        {
+            var updatedEntity1 = new EntityWithList
+            {
+                MyList = new List<ListItem>
+                {
+                    new() { Value = "My First Value" },
+                    new() { Value = "My Second Value" }
+                }
+            };
+
+            chain.Add(initialEntity, updatedEntity1, keyDate1);
+            chain.Count.Should().Be(2); // [-infinity, keyDate1); [keyDate1, +infinity)
+            ReverseAndRevert(chain, initialEntity);
+        }
+        (var antiparallelInitialEntity, var antiparallelChain) = chain.Reverse(initialEntity);
+        antiparallelInitialEntity.Should().Match<EntityWithList>(x => x.MyList.Count == 2, because: "Initially the list had 2 items");
+        var patchingACorrectInitialEntity = () => antiparallelChain.PatchToDate(antiparallelInitialEntity, keyDate1 - TimeSpan.FromDays(10));
+        patchingACorrectInitialEntity.Should().NotThrow();
+
+        var corruptedInitialEntity = antiparallelInitialEntity; // we modify the reference here, but that's fine. We improve the readability but don't re-use the antiparallelInitialEntity anywhere downstream.
+        corruptedInitialEntity.MyList.RemoveAt(1);
+        var applyingPatchesToACorruptedInitialEntity = () => antiparallelChain.PatchToDate(corruptedInitialEntity, keyDate1 - TimeSpan.FromDays(10));
+        applyingPatchesToACorruptedInitialEntity.Should().ThrowExactly<ArgumentOutOfRangeException>();
+    }
+
+    private static void ReverseAndRevert(TimeRangePatchChain<EntityWithList> chain, EntityWithList initialEntity)
+    {
+        var (reverseEntity, reverseChain) = chain.Reverse(initialEntity);
+        var (rereverseEntity, rereverseChain) = reverseChain.Reverse(reverseEntity);
+        rereverseChain.Should().BeEquivalentTo(chain);
+        initialEntity.Should().BeEquivalentTo(rereverseEntity);
+    }
+}