Fix item-at Satisfies source typing

TUnit.Assertions.Tests/Bugs/Issue5706Tests.cs

@@ -0,0 +1,88 @@
+namespace TUnit.Assertions.Tests.Bugs;
+
+/// <summary>
+/// Regression tests for GitHub issue #5706:
+/// ItemAt(...).Satisfies(...) should preserve specialised assertion sources for
+/// collection-like item values instead of exposing only IAssertionSource&lt;TItem&gt;.
+/// </summary>
+public class Issue5706Tests
+{
+    [Test]
+    public async Task List_ItemAt_Satisfies_Preserves_String_Item_Source()
+    {
+        IList<string> items = new List<string> { "alpha" };
+
+        await Assert.That(items).ItemAt(0).Satisfies(item => item.Contains("pha"));
+    }
+
+    [Test]
+    public async Task List_ItemAt_Satisfies_Preserves_Collection_Item_Source()
+    {
+        IList<IEnumerable<int>> items = new List<IEnumerable<int>> { new[] { 1, 2, 3 } };
+
+        await Assert.That(items).ItemAt(0).Satisfies(item => item.Count().IsEqualTo(3));
+    }
+
+    [Test]
+    public async Task List_ItemAt_Satisfies_Preserves_Dictionary_Item_Source()
+    {
+        IList<IDictionary<string, int>> items = new List<IDictionary<string, int>>
+        {
+            new Dictionary<string, int> { ["answer"] = 42 }
+        };
+
+        await Assert.That(items).ItemAt(0).Satisfies(item => item.ContainsKey("answer"));
+    }
+
+    [Test]
+    public async Task List_ItemAt_Satisfies_Preserves_Set_Item_Source()
+    {
+        IList<ISet<int>> items = new List<ISet<int>>
+        {
+            new HashSet<int> { 1, 2, 3 }
+        };
+
+        await Assert.That(items).ItemAt(0).Satisfies(item => item.IsSupersetOf(new[] { 1, 2 }));
+    }
+
+    [Test]
+    public async Task ReadOnlyList_ItemAt_Satisfies_Preserves_String_Item_Source()
+    {
+        IReadOnlyList<string> items = new List<string> { "alpha" };
+
+        await Assert.That(items).ItemAt(0).Satisfies(item => item.Contains("pha"));
+    }
+
+    [Test]
+    public async Task ReadOnlyList_ItemAt_Satisfies_Preserves_Collection_Item_Source()
+    {
+        IReadOnlyList<List<int>> items = new List<List<int>>
+        {
+            new() { 1, 2, 3 }
+        };
+
+        await Assert.That(items).ItemAt(0).Satisfies(item => item.Count().IsEqualTo(3));
+    }
+
+    [Test]
+    public async Task ReadOnlyList_ItemAt_Satisfies_Preserves_Dictionary_Item_Source()
+    {
+        IReadOnlyList<Dictionary<string, int>> items = new List<Dictionary<string, int>>
+        {
+            new() { ["answer"] = 42 }
+        };
+
+        await Assert.That(items).ItemAt(0).Satisfies(item => item.ContainsKey("answer"));
+    }
+
+    [Test]
+    public async Task ReadOnlyList_ItemAt_Satisfies_Preserves_Set_Item_Source()
+    {
+        IReadOnlyList<HashSet<int>> items = new List<HashSet<int>>
+        {
+            new() { 1, 2, 3 }
+        };
+
+        await Assert.That(items).ItemAt(0).Satisfies(item => item.IsSupersetOf(new[] { 1, 2 }));
+    }
+}

TUnit.Assertions/Conditions/ListAssertions.cs

@@ -67,6 +67,10 @@ public class ListItemAtSource<TList, TItem> : IAssertionSource<TItem>
     private readonly AssertionContext<TList> _listContext;
     private readonly int _index;
 
+    internal AssertionContext<TList> InternalListContext => _listContext;
+
+    internal int InternalIndex => _index;
+
     public AssertionContext<TItem> Context { get; }
 
     public ListItemAtSource(AssertionContext<TList> listContext, int index)
@@ -420,12 +424,23 @@ public class ListItemAtSatisfiesAssertion<TList, TItem> : ListAssertionBase<TLis
     where TList : IList<TItem>
 {
     private readonly int _index;
-    private readonly Func<IAssertionSource<TItem>, Assertion<TItem>?> _assertion;
+    private readonly Func<TItem, int, IAssertion?> _assertion;
 
     public ListItemAtSatisfiesAssertion(
         AssertionContext<TList> context,
         int index,
         Func<IAssertionSource<TItem>, Assertion<TItem>?> assertion)
+        : this(
+            context,
+            index,
+            (item, itemIndex) => assertion(new ValueAssertion<TItem>(item, $"item[{itemIndex}]")))
+    {
+    }
+
+    internal ListItemAtSatisfiesAssertion(
+        AssertionContext<TList> context,
+        int index,
+        Func<TItem, int, IAssertion?> assertion)
         : base(context)
     {
         _index = index;
@@ -451,8 +466,7 @@ protected override async Task<AssertionResult> CheckAsync(EvaluationMetadata<TLi
         }
 
         var actualItem = metadata.Value[_index];
-        var itemSource = new ValueAssertion<TItem>(actualItem, $"item[{_index}]");
-        var resultingAssertion = _assertion(itemSource);
+        var resultingAssertion = _assertion(actualItem, _index);
 
         if (resultingAssertion != null)
         {

TUnit.Assertions/Conditions/ReadOnlyListAssertions.cs

@@ -69,6 +69,10 @@ public class ReadOnlyListItemAtSource<TList, TItem> : IAssertionSource<TItem>
     private readonly AssertionContext<TList> _listContext;
     private readonly int _index;
 
+    internal AssertionContext<TList> InternalListContext => _listContext;
+
+    internal int InternalIndex => _index;
+
     public AssertionContext<TItem> Context { get; }
 
     public ReadOnlyListItemAtSource(AssertionContext<TList> listContext, int index)
@@ -422,12 +426,23 @@ public class ReadOnlyListItemAtSatisfiesAssertion<TList, TItem> : ReadOnlyListAs
     where TList : IReadOnlyList<TItem>
 {
     private readonly int _index;
-    private readonly Func<IAssertionSource<TItem>, Assertion<TItem>?> _assertion;
+    private readonly Func<TItem, int, IAssertion?> _assertion;
 
     public ReadOnlyListItemAtSatisfiesAssertion(
         AssertionContext<TList> context,
         int index,
         Func<IAssertionSource<TItem>, Assertion<TItem>?> assertion)
+        : this(
+            context,
+            index,
+            (item, itemIndex) => assertion(new ValueAssertion<TItem>(item, $"item[{itemIndex}]")))
+    {
+    }
+
+    internal ReadOnlyListItemAtSatisfiesAssertion(
+        AssertionContext<TList> context,
+        int index,
+        Func<TItem, int, IAssertion?> assertion)
         : base(context)
     {
         _index = index;
@@ -453,8 +468,7 @@ protected override async Task<AssertionResult> CheckAsync(EvaluationMetadata<TLi
         }
 
         var actualItem = metadata.Value[_index];
-        var itemSource = new ValueAssertion<TItem>(actualItem, $"item[{_index}]");
-        var resultingAssertion = _assertion(itemSource);
+        var resultingAssertion = _assertion(actualItem, _index);
 
         if (resultingAssertion != null)
         {