fix(assertions): prefer string overload of Member() over IEnumerable<char> (#5702)

TUnit.Assertions.Tests/Bugs/Issue5702Tests.cs

@@ -0,0 +1,60 @@
+namespace TUnit.Assertions.Tests.Bugs;
+
+/// <summary>
+/// Regression tests for GitHub issue #5702:
+/// `.Member(x => x.StringProperty, p => p.IsEqualTo("..."))` incorrectly resolved the
+/// collection `Member&lt;TObject, TItem&gt;` overload (TItem=char) instead of the general
+/// `Member&lt;TObject, TMember&gt;` (TMember=string) overload because the collection
+/// overload carries a higher `[OverloadResolutionPriority]`. The resulting
+/// `IAssertionSource&lt;IEnumerable&lt;char&gt;&gt;` triggers TUnitAssertions0016 and
+/// uses reference equality on strings, so non-interned but equal strings fail.
+/// </summary>
+public class Issue5702Tests
+{
+    [Test]
+    public async Task Member_On_String_Property_Uses_String_Equality_Not_Reference()
+    {
+        var value = KeyValuePair.Create<string, object?>(NonInterned("error"), null);
+
+        await Assert.That(value).Member(kvp => kvp.Key, key => key.IsEqualTo(NonInterned("error")));
+    }
+
+    [Test]
+    public async Task Member_On_String_Property_With_Nested_Object()
+    {
+        var model = new Wrapper { Name = NonInterned("hello") };
+
+        await Assert.That(model).Member(m => m.Name, n => n.IsEqualTo(NonInterned("hello")));
+    }
+
+    [Test]
+    public async Task Member_On_String_Property_Composes_With_And_Chaining()
+    {
+        var model = new Wrapper { Name = NonInterned("hello"), Count = 42 };
+
+        await Assert.That(model)
+            .Member(m => m.Name, n => n.IsEqualTo(NonInterned("hello")))
+            .And.Member(m => m.Count, c => c.IsEqualTo(42));
+    }
+
+    [Test]
+    public async Task Member_On_NonString_IEnumerableChar_Still_Uses_Collection_Overload()
+    {
+        var model = new WithChars { Chars = ['h', 'i'] };
+
+        await Assert.That(model).Member(m => m.Chars, c => c.Contains('h'));
+    }
+
+    private static string NonInterned(string s) => new(s.ToCharArray());
+
+    private sealed class Wrapper
+    {
+        public string Name { get; set; } = string.Empty;
+        public int Count { get; set; }
+    }
+
+    private sealed class WithChars
+    {
+        public IEnumerable<char> Chars { get; set; } = [];
+    }
+}

TUnit.Assertions/Extensions/AssertionExtensions.cs

@@ -282,6 +282,46 @@ public static MemberAssertionResult<TObject> Member<TObject, TKey, TValue>(
         return BuildMemberResult(parentContext, pendingAssertion, combinerType, erasedAssertion);
     }
 
+    /// <summary>
+    /// Asserts on a string member of an object using a lambda selector and assertion lambda.
+    /// This overload takes priority over the collection overload so that `string` is treated as a
+    /// scalar value rather than an `IEnumerable&lt;char&gt;`.
+    /// Example: await Assert.That(obj).Member(x => x.Name, n => n.IsEqualTo("expected"));
+    /// </summary>
+    [OverloadResolutionPriority(3)]
+    public static MemberAssertionResult<TObject> Member<TObject, TTransformed>(
+        this IAssertionSource<TObject> source,
+        Expression<Func<TObject, string?>> memberSelector,
+        Func<IAssertionSource<string>, Assertion<TTransformed>> assertions)
+        => Member<TObject, string, TTransformed>(source, memberSelector, assertions);
+
+    /// <summary>
+    /// Asserts on a string member of an object using a lambda selector and assertion lambda.
+    /// This overload takes priority over the collection overload so that `string` is treated as a
+    /// scalar value rather than an `IEnumerable&lt;char&gt;`.
+    /// </summary>
+    [OverloadResolutionPriority(3)]
+    public static MemberAssertionResult<TObject> Member<TObject>(
+        this IAssertionSource<TObject> source,
+        Expression<Func<TObject, string?>> memberSelector,
+        Func<IAssertionSource<string>, Assertion<string>> assertions)
+        => Member<TObject, string>(source, memberSelector, assertions);
+
+    /// <summary>
+    /// Asserts on a string member of an object using a lambda selector and assertion lambda
+    /// that returns an untyped assertion (for extension methods returning non-<see cref="Assertion{T}"/> types).
+    /// This overload takes priority over the collection overload so that `string` is treated as a
+    /// scalar value rather than an `IEnumerable&lt;char&gt;`.
+    /// Note: For AOT compatibility, use the TTransformed overload instead.
+    /// </summary>
+    [OverloadResolutionPriority(3)]
+    [RequiresDynamicCode("Uses reflection for legacy compatibility. For AOT compatibility, use the Member<TObject, TTransformed> overload with strongly-typed assertions.")]
+    public static MemberAssertionResult<TObject> Member<TObject>(
+        this IAssertionSource<TObject> source,
+        Expression<Func<TObject, string?>> memberSelector,
+        Func<IAssertionSource<string>, object> assertions)
+        => Member<TObject, string>(source, memberSelector, assertions);
+
     /// <summary>
     /// Asserts on a collection member of an object using a lambda selector and assertion lambda.
     /// The assertion lambda receives collection assertion methods (Count, Contains, IsEmpty, etc.).

TUnit.PublicAPI/Tests.Assertions_Library_Has_No_API_Changes.DotNet10_0.verified.txt

@@ -2693,6 +2693,12 @@ namespace .Extensions
             where TValue :  struct, <TValue> { }
         public static . Length(this .<string> source) { }
         public static . Length(this .<string> source, <.<int>, .<int>?> lengthAssertion, [.("lengthAssertion")] string? expression = null) { }
+        [.(3)]
+        public static .<TObject> Member<TObject>(this .<TObject> source, .<<TObject, string?>> memberSelector, <.<string>, .<string>> assertions) { }
+        [.("Uses reflection for legacy compatibility. For AOT compatibility, use the Member<T" +
+            "Object, TTransformed> overload with strongly-typed assertions.")]
+        [.(3)]
+        public static .<TObject> Member<TObject>(this .<TObject> source, .<<TObject, string?>> memberSelector, <.<string>, object> assertions) { }
         [.(1)]
         public static .<TObject> Member<TObject, TItem>(this .<TObject> source, .<<TObject, .<TItem>>> memberSelector, <.<.<TItem>, TItem>, .<.<TItem>>> assertions) { }
         [.("Uses reflection for legacy compatibility. For AOT compatibility, use the Member<T" +
@@ -2713,6 +2719,8 @@ namespace .Extensions
         [.("Uses reflection for legacy compatibility. For AOT compatibility, use the Member<T" +
             "Object, TMember, TTransformed> overload with strongly-typed assertions.")]
         public static .<TObject> Member<TObject, TMember>(this .<TObject> source, .<<TObject, TMember?>> memberSelector, <.<TMember>, object> assertions) { }
+        [.(3)]
+        public static .<TObject> Member<TObject, TTransformed>(this .<TObject> source, .<<TObject, string?>> memberSelector, <.<string>, .<TTransformed>> assertions) { }
         [.(2)]
         public static .<TObject> Member<TObject, TItem, TTransformed>(this .<TObject> source, .<<TObject, .<TItem>>> memberSelector, <.<.<TItem>, TItem>, .<TTransformed>> assertions) { }
         [.(2)]

TUnit.PublicAPI/Tests.Assertions_Library_Has_No_API_Changes.DotNet8_0.verified.txt

@@ -2672,6 +2672,10 @@ namespace .Extensions
             where TValue :  struct, <TValue> { }
         public static . Length(this .<string> source) { }
         public static . Length(this .<string> source, <.<int>, .<int>?> lengthAssertion, [.("lengthAssertion")] string? expression = null) { }
+        public static .<TObject> Member<TObject>(this .<TObject> source, .<<TObject, string?>> memberSelector, <.<string>, .<string>> assertions) { }
+        [.("Uses reflection for legacy compatibility. For AOT compatibility, use the Member<T" +
+            "Object, TTransformed> overload with strongly-typed assertions.")]
+        public static .<TObject> Member<TObject>(this .<TObject> source, .<<TObject, string?>> memberSelector, <.<string>, object> assertions) { }
         public static .<TObject> Member<TObject, TItem>(this .<TObject> source, .<<TObject, .<TItem>>> memberSelector, <.<.<TItem>, TItem>, .<.<TItem>>> assertions) { }
         [.("Uses reflection for legacy compatibility. For AOT compatibility, use the Member<T" +
             "Object, TItem, TTransformed> overload with strongly-typed assertions.")]
@@ -2688,6 +2692,7 @@ namespace .Extensions
         [.("Uses reflection for legacy compatibility. For AOT compatibility, use the Member<T" +
             "Object, TMember, TTransformed> overload with strongly-typed assertions.")]
         public static .<TObject> Member<TObject, TMember>(this .<TObject> source, .<<TObject, TMember?>> memberSelector, <.<TMember>, object> assertions) { }
+        public static .<TObject> Member<TObject, TTransformed>(this .<TObject> source, .<<TObject, string?>> memberSelector, <.<string>, .<TTransformed>> assertions) { }
         public static .<TObject> Member<TObject, TItem, TTransformed>(this .<TObject> source, .<<TObject, .<TItem>>> memberSelector, <.<.<TItem>, TItem>, .<TTransformed>> assertions) { }
         public static .<TObject> Member<TObject, TKey, TValue>(this .<TObject> source, .<<TObject, .<TKey, TValue>>> memberSelector, <.<.<TKey, TValue>, TKey, TValue>, .<.<TKey, TValue>>> assertions)
             where TKey :  notnull { }

TUnit.PublicAPI/Tests.Assertions_Library_Has_No_API_Changes.DotNet9_0.verified.txt

@@ -2693,6 +2693,12 @@ namespace .Extensions
             where TValue :  struct, <TValue> { }
         public static . Length(this .<string> source) { }
         public static . Length(this .<string> source, <.<int>, .<int>?> lengthAssertion, [.("lengthAssertion")] string? expression = null) { }
+        [.(3)]
+        public static .<TObject> Member<TObject>(this .<TObject> source, .<<TObject, string?>> memberSelector, <.<string>, .<string>> assertions) { }
+        [.("Uses reflection for legacy compatibility. For AOT compatibility, use the Member<T" +
+            "Object, TTransformed> overload with strongly-typed assertions.")]
+        [.(3)]
+        public static .<TObject> Member<TObject>(this .<TObject> source, .<<TObject, string?>> memberSelector, <.<string>, object> assertions) { }
         [.(1)]
         public static .<TObject> Member<TObject, TItem>(this .<TObject> source, .<<TObject, .<TItem>>> memberSelector, <.<.<TItem>, TItem>, .<.<TItem>>> assertions) { }
         [.("Uses reflection for legacy compatibility. For AOT compatibility, use the Member<T" +
@@ -2713,6 +2719,8 @@ namespace .Extensions
         [.("Uses reflection for legacy compatibility. For AOT compatibility, use the Member<T" +
             "Object, TMember, TTransformed> overload with strongly-typed assertions.")]
         public static .<TObject> Member<TObject, TMember>(this .<TObject> source, .<<TObject, TMember?>> memberSelector, <.<TMember>, object> assertions) { }
+        [.(3)]
+        public static .<TObject> Member<TObject, TTransformed>(this .<TObject> source, .<<TObject, string?>> memberSelector, <.<string>, .<TTransformed>> assertions) { }
         [.(2)]
         public static .<TObject> Member<TObject, TItem, TTransformed>(this .<TObject> source, .<<TObject, .<TItem>>> memberSelector, <.<.<TItem>, TItem>, .<TTransformed>> assertions) { }
         [.(2)]

TUnit.PublicAPI/Tests.Assertions_Library_Has_No_API_Changes.Net4_7.verified.txt

@@ -2418,6 +2418,8 @@ namespace .Extensions
             where TValue :  struct, <TValue> { }
         public static . Length(this .<string> source) { }
         public static . Length(this .<string> source, <.<int>, .<int>?> lengthAssertion, [.("lengthAssertion")] string? expression = null) { }
+        public static .<TObject> Member<TObject>(this .<TObject> source, .<<TObject, string?>> memberSelector, <.<string>, .<string>> assertions) { }
+        public static .<TObject> Member<TObject>(this .<TObject> source, .<<TObject, string?>> memberSelector, <.<string>, object> assertions) { }
         public static .<TObject> Member<TObject, TItem>(this .<TObject> source, .<<TObject, .<TItem>>> memberSelector, <.<.<TItem>, TItem>, .<.<TItem>>> assertions) { }
         public static .<TObject> Member<TObject, TItem>(this .<TObject> source, .<<TObject, .<TItem>>> memberSelector, <.<.<TItem>, TItem>, object> assertions) { }
         public static .<TObject> Member<TObject, TMember>(this .<TObject> source, .<<TObject, .<TMember>>> memberSelector, <.<TMember>, .<TMember>> assertions) { }
@@ -2426,6 +2428,7 @@ namespace .Extensions
         public static .<TObject> Member<TObject, TMember>(this .<TObject> source, .<<TObject, .<TMember>>> memberSelector, <.<TMember>, object> assertions) { }
         public static .<TObject> Member<TObject, TMember>(this .<TObject> source, .<<TObject, TMember?>> memberSelector, <.<TMember>, .<TMember>> assertions) { }
         public static .<TObject> Member<TObject, TMember>(this .<TObject> source, .<<TObject, TMember?>> memberSelector, <.<TMember>, object> assertions) { }
+        public static .<TObject> Member<TObject, TTransformed>(this .<TObject> source, .<<TObject, string?>> memberSelector, <.<string>, .<TTransformed>> assertions) { }
         public static .<TObject> Member<TObject, TItem, TTransformed>(this .<TObject> source, .<<TObject, .<TItem>>> memberSelector, <.<.<TItem>, TItem>, .<TTransformed>> assertions) { }
         public static .<TObject> Member<TObject, TKey, TValue>(this .<TObject> source, .<<TObject, .<TKey, TValue>>> memberSelector, <.<.<TKey, TValue>, TKey, TValue>, .<.<TKey, TValue>>> assertions)
             where TKey :  notnull { }