Fix IsTypeOf<>() to work with all types and improve array overload resolution

TUnit.Assertions.Tests/TypeOfTests.cs

@@ -13,4 +13,60 @@ public async Task Returns_Casted_Object()
 
         await Assert.That(result).IsNotNull();
     }
+
+    [Test]
+    public async Task IsTypeOf_Works_With_NonObject_Type()
+    {
+        // This test verifies the fix for the issue where IsTypeOf only worked with object types
+        string str = "Hello";
+
+        var result = await Assert.That(str).IsTypeOf<string, string>();
+
+        await Assert.That(result).IsEqualTo("Hello");
+    }
+
+    [Test]
+    public async Task IsTypeOf_Works_With_Object_SingleTypeParameter()
+    {
+        object obj = "Hello";
+
+        var result = await Assert.That(obj).IsTypeOf<string>();
+
+        await Assert.That(result).IsEqualTo("Hello");
+    }
+
+    [Test]
+    public async Task IsTypeOf_Works_With_NullableObject()
+    {
+        object? nullableObj = new StringBuilder("Test");
+
+        var result = await Assert.That(nullableObj).IsTypeOf<StringBuilder>();
+
+        await Assert.That(result.ToString()).IsEqualTo("Test");
+    }
+
+    [Test]
+    public async Task IsTypeOf_Fails_When_Type_Mismatch()
+    {
+        object obj = "Hello";
+
+        await Assert.ThrowsAsync<TUnit.Assertions.Exceptions.AssertionException>(async () =>
+        {
+            await Assert.That(obj).IsTypeOf<int>();
+        });
+    }
+
+    [Test]
+    public async Task IsTypeOf_TwoTypeParameters_Works_With_AnySourceType()
+    {
+        // Test with string as source type
+        string str = "Hello";
+        var result1 = await Assert.That(str).IsTypeOf<string, string>();
+        await Assert.That(result1).IsEqualTo("Hello");
+
+        // Test with int as source type
+        int number = 42;
+        var result2 = await Assert.That(number).IsTypeOf<int, int>();
+        await Assert.That(result2).IsEqualTo(42);
+    }
 }

TUnit.Assertions/Extensions/Assert.cs

@@ -63,15 +63,15 @@ public static DictionaryAssertion<TKey, TValue> That<TKey, TValue>(
     }
 
     /// <summary>
-    /// Creates an assertion for an array.
+    /// Creates an assertion for an array (nullable or non-nullable).
     /// This overload enables better type inference for collection operations like IsInOrder, All, ContainsOnly.
     /// Example: await Assert.That(array).IsInOrder();
     /// </summary>
     public static CollectionAssertion<TItem> That<TItem>(
-        TItem[] value,
+        TItem[]? value,
         [CallerArgumentExpression(nameof(value))] string? expression = null)
     {
-        return new CollectionAssertion<TItem>(value, expression);
+        return new CollectionAssertion<TItem>(value!, expression);
     }
 
     /// <summary>

TUnit.Assertions/Extensions/AssertionExtensions.cs

@@ -357,25 +357,26 @@ public static Chaining.OrAssertion<TValue> IsNotEqualTo<TValue>(
     // IsTypeOf(Type), IsAssignableTo, IsNotAssignableTo are now generated by AssertionExtensionGenerator
 
     /// <summary>
-    /// Asserts that the value is of the specified type and returns an assertion on the casted value (specialized for object).
+    /// Asserts that the value is of the specified type and returns an assertion on the casted value.
     /// Example: await Assert.That(obj).IsTypeOf<StringBuilder>();
+    /// This generic overload works with any source type.
     /// </summary>
-    public static TypeOfAssertion<object, TExpected> IsTypeOf<TExpected>(
-        this IAssertionSource<object> source)
+    public static TypeOfAssertion<TValue, TExpected> IsTypeOf<TExpected, TValue>(
+        this IAssertionSource<TValue> source)
     {
         source.Context.ExpressionBuilder.Append($".IsTypeOf<{typeof(TExpected).Name}>()");
-        return new TypeOfAssertion<object, TExpected>(source.Context);
+        return new TypeOfAssertion<TValue, TExpected>(source.Context);
     }
 
     /// <summary>
-    /// Asserts that the value is of the specified type and returns an assertion on the casted value.
+    /// Asserts that the value is of the specified type and returns an assertion on the casted value (specialized for object).
     /// Example: await Assert.That(obj).IsTypeOf<StringBuilder>();
     /// </summary>
-    public static TypeOfAssertion<TFrom, TTo> IsTypeOf<TTo, TFrom>(
-        this IAssertionSource<TFrom> source)
+    public static TypeOfAssertion<object, TExpected> IsTypeOf<TExpected>(
+        this IAssertionSource<object> source)
     {
-        source.Context.ExpressionBuilder.Append($".IsTypeOf<{typeof(TTo).Name}>()");
-        return new TypeOfAssertion<TFrom, TTo>(source.Context);
+        source.Context.ExpressionBuilder.Append($".IsTypeOf<{typeof(TExpected).Name}>()");
+        return new TypeOfAssertion<object, TExpected>(source.Context);
     }
 
     /// <summary>