fix: Allow Item.Member after HasSingleItem

src/TUnit.Assertions/Conditions/MemberAssertion.cs

@@ -132,10 +132,10 @@ public TypeErasedAssertion(Assertion<T> innerAssertion)
         _innerAssertion = innerAssertion ?? throw new ArgumentNullException(nameof(innerAssertion));
     }
 
-    public override async Task<object?> AssertAsync()
+    protected override async Task<AssertionResult> CheckAsync(EvaluationMetadata<object?> metadata)
     {
         await _innerAssertion.AssertAsync();
-        return null;
+        return AssertionResult.Passed;
     }
 
     protected override string GetExpectation() => _innerAssertion.InternalGetExpectation();

tests/TUnit.Assertions.Tests/Bugs/Issue6581Tests.cs

@@ -0,0 +1,36 @@
+namespace TUnit.Assertions.Tests.Bugs;
+
+public class Issue6581Tests
+{
+    [Test]
+    public async Task Member_After_HasSingleItem_Item_Succeeds()
+    {
+        var items = new List<TestObject>
+        {
+            new() { Value = 4 }
+        };
+
+        await Assert
+            .That(items).HasSingleItem()
+            .Item.Member(item => item.Value, value => value.IsEqualTo(4));
+    }
+
+    [Test]
+    public async Task Member_After_HasSingleItem_With_Predicate_Item_Succeeds()
+    {
+        var items = new List<TestObject>
+        {
+            new() { Value = 3 },
+            new() { Value = 4 }
+        };
+
+        await Assert
+            .That(items).HasSingleItem(item => item.Value == 4)
+            .Item.Member(item => item.Value, value => value.IsEqualTo(4));
+    }
+
+    private sealed class TestObject
+    {
+        public int Value { get; init; }
+    }
+}