diff --git a/src/tests/Interop/StringMarshalling/UTF8/UTF8Test.cs b/src/tests/Interop/StringMarshalling/UTF8/UTF8Test.cs
index 44decce077a698..3dfcd9efa2de86 100644
--- a/src/tests/Interop/StringMarshalling/UTF8/UTF8Test.cs
+++ b/src/tests/Interop/StringMarshalling/UTF8/UTF8Test.cs
@@ -7,281 +7,217 @@
 using System.Collections.Generic;
 using Xunit;
 
-// UTF8
-class UTF8StringTests
+namespace StringMarshaling
 {
-    [DllImport("UTF8TestNative", CallingConvention = CallingConvention.Cdecl)]
-    [return: MarshalAs(UnmanagedType.LPUTF8Str)]
-    public static extern string StringParameterInOut([In, Out][MarshalAs(UnmanagedType.LPUTF8Str)]string s, int index);
-    public static void TestInOutStringParameter(string orgString, int index)
+    [OuterLoop]
+    [ActiveIssue("https://github.com/dotnet/runtime/issues/91388", typeof(TestLibrary.PlatformDetection), nameof(TestLibrary.PlatformDetection.PlatformDoesNotSupportNativeTestAssets))]
+    public class UTF8Tests
     {
-        string passedString = orgString;
-        string expectedNativeString = passedString;
+        [DllImport("UTF8TestNative", CallingConvention = CallingConvention.Cdecl)]
+        [return: MarshalAs(UnmanagedType.LPUTF8Str)]
+        static extern string StringParameterInOut([In, Out][MarshalAs(UnmanagedType.LPUTF8Str)] string s, int index);
+
+        [DllImport("UTF8TestNative", CallingConvention = CallingConvention.Cdecl)]
+        [return: MarshalAs(UnmanagedType.LPUTF8Str)]
+        static extern string StringParameterOut([Out][MarshalAs(UnmanagedType.LPUTF8Str)] string s, int index);
+
+        [DllImport("UTF8TestNative", CallingConvention = CallingConvention.Cdecl)]
+        static extern void StringParameterRefOut([MarshalAs(UnmanagedType.LPUTF8Str)] out string s, int index);
+
+        [DllImport("UTF8TestNative", CallingConvention = CallingConvention.Cdecl)]
+        [return: MarshalAs(UnmanagedType.Bool)]
+        static extern bool StringParameterRef([MarshalAs(UnmanagedType.LPUTF8Str)] ref string s, int index);
+
+        [DllImport("UTF8TestNative", CallingConvention = CallingConvention.Cdecl)]
+        [return: MarshalAs(UnmanagedType.Bool)]
+        static extern bool StringBuilderParameterInOut([In, Out][MarshalAs(UnmanagedType.LPUTF8Str)] StringBuilder s, int index);
+
+        [DllImport("UTF8TestNative", CallingConvention = CallingConvention.Cdecl)]
+        static extern void StringBuilderParameterOut([Out][MarshalAs(UnmanagedType.LPUTF8Str)] StringBuilder s, int index);
+
+        [DllImport("UTF8TestNative", CallingConvention = CallingConvention.Cdecl)]
+        [return: MarshalAs(UnmanagedType.LPUTF8Str, SizeConst = 512)]
+        static extern StringBuilder StringBuilderParameterReturn(int index);
+
+        [DllImport("UTF8TestNative", CallingConvention = CallingConvention.Cdecl)]
+        [return: MarshalAs(UnmanagedType.Bool)]
+        static extern bool TestStructWithUtf8Field(Utf8Struct utfStruct);
+
+        [DllImport("UTF8TestNative", CallingConvention = CallingConvention.Cdecl)]
+        static extern void SetStringInStruct(ref Utf8Struct utfStruct, [MarshalAs(UnmanagedType.LPUTF8Str)] string str);
+
+        [DllImport("UTF8TestNative", CallingConvention = CallingConvention.Cdecl)]
+        static extern void Utf8DelegateAsParameter(DelegateUTF8Parameter param);
 
-        string nativeString = StringParameterInOut(passedString, index);
-        if (!(nativeString == expectedNativeString))
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
+        public delegate void DelegateUTF8Parameter([MarshalAs(UnmanagedType.LPUTF8Str)] string utf8String, int index);
+
+        public struct Utf8Struct
         {
-            throw new Exception("StringParameterInOut: nativeString != expectedNativeString ");
+            [MarshalAs(UnmanagedType.LPUTF8Str)]
+            public string FirstName;
+            public int index;
         }
-    }
 
-    [DllImport("UTF8TestNative", CallingConvention = CallingConvention.Cdecl)]
-    [return: MarshalAs(UnmanagedType.LPUTF8Str)]
-    public static extern string StringParameterOut([Out][MarshalAs(UnmanagedType.LPUTF8Str)]string s, int index);
-    public static void TestOutStringParameter(string orgString, int index)
-    {
-        string passedString = orgString;
-        string expectedNativeString = passedString;
-        string nativeString = StringParameterInOut(passedString, index);
-        if (!(nativeString == expectedNativeString))
+        unsafe struct UnmanagedStruct
         {
-            throw new Exception("StringParameterInOut: nativeString != expectedNativeString ");
+            public fixed byte psz[8];
         }
-    }
 
-    [DllImport("UTF8TestNative", CallingConvention = CallingConvention.Cdecl)]
-    public static extern void StringParameterRefOut([MarshalAs(UnmanagedType.LPUTF8Str)]out string s, int index);
-    public static void TestStringPassByOut(string orgString, int index)
-    {
-        // out string
-        string expectedNative = string.Empty;
-        StringParameterRefOut(out expectedNative, index);
-        if (orgString != expectedNative)
+        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
+        struct ManagedStruct
         {
-            throw new Exception("TestStringPassByOut : expectedNative != outString");
+            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 8)]
+            public string str;
         }
-    }
 
-    [DllImport("UTF8TestNative", CallingConvention = CallingConvention.Cdecl)]
-    public static extern void StringParameterRef([MarshalAs(UnmanagedType.LPUTF8Str)]ref string s, int index);
-    public static void TestStringPassByRef(string orgString, int index)
-    {
-        string orgCopy = new string(orgString.ToCharArray());
-        StringParameterRef(ref orgString, index);
-        if (orgString != orgCopy)
+        public static readonly string[] Utf8Strings =
+        {
+            "Managed",
+            "S\u00EEne kl\u00E2wen durh die wolken sint geslagen",
+            "\u0915\u093E\u091A\u0902 \u0936\u0915\u094D\u0928\u094B\u092E\u094D\u092F\u0924\u094D\u0924\u0941\u092E\u094D \u0964 \u0928\u094B\u092A\u0939\u093F\u0928\u0938\u094D\u0924\u093F \u092E\u093E\u092E\u094D",
+            "\u6211\u80FD\u541E\u4E0B\u73BB\u7483\u800C\u4E0D\u4F24\u8EAB\u4F53",
+            "\u10E6\u10DB\u10D4\u10E0\u10D7\u10E1\u10D8 \u10E8\u10D4\u10DB\u10D5\u10D4\u10D3\u10E0\u10D4,\u10E8\u10D4\u10DB\u10D5\u10D4\u10D3\u10E0\u10D4, \u10DC\u10E3\u10D7\u10E3 \u10D9\u10D5\u10DA\u10D0 \u10D3\u10D0\u10DB\u10EE\u10E1\u10DC\u10D0\u10E1 \u10E8\u10D4\u10DB\u10D5\u10D4\u10D3\u10E0\u10D4,\u10E1\u10DD\u10E4\u10DA\u10D8\u10E1\u10D0 \u10E8\u10D4\u10DB\u10D5\u10D4\u10D3\u10E0\u10D4, \u10E8\u10D4\u10DB\u10D5\u10D4\u10D3\u10E0\u10D4,\u10E8\u10D4\u10DB\u10D5\u10D4\u10D3\u10E0\u10D4,\u10E8\u10D4\u10DB\u10D5\u10D4\u10D3\u10E0\u10D4,\u10E8\u10E0\u10DD\u10DB\u10D0\u10E1\u10D0, \u10EA\u10D4\u10EA\u10EE\u10DA\u10E1, \u10EC\u10E7\u10D0\u10DA\u10E1\u10D0 \u10D3\u10D0 \u10DB\u10D8\u10EC\u10D0\u10E1\u10D0, \u10F0\u10D0\u10D4\u10E0\u10D7\u10D0 \u10D7\u10D0\u10DC\u10D0 \u10DB\u10E0\u10DD\u10DB\u10D0\u10E1\u10D0; \u10DB\u10DD\u10DB\u10EA\u10DC\u10D4\u10E1 \u10E4\u10E0\u10D7\u10D4\u10DC\u10D8 \u10D3\u10D0 \u10D0\u10E6\u10D5\u10E4\u10E0\u10D8\u10DC\u10D3\u10D4, \u10DB\u10D8\u10D5\u10F0\u10EE\u10D5\u10D3\u10D4 \u10DB\u10D0\u10E1 \u10E9\u10D4\u10DB\u10E1\u10D0 \u10DC\u10D3\u10DD\u10DB\u10D0\u10E1\u10D0, \u10D3\u10E6\u10D8\u10E1\u10D8\u10D7 \u10D3\u10D0 \u10E6\u10D0\u10DB\u10D8\u10D7 \u10D5\u10F0\u10EE\u10D4\u10D3\u10D5\u10D8\u10D3\u10D4 \u10DB\u10D6\u10D8\u10E1\u10D0 \u10D4\u10DA\u10D5\u10D0\u10D7\u10D0 \u10D9\u10E0\u10D7\u10DD\u10DB\u10D0\u10D0\u10E1\u10D0\u10E8\u10D4\u10DB\u10D5\u10D4\u10D3\u10E0\u10D4,\u10E8\u10D4\u10DB\u10D5\u10D4\u10D3\u10E0\u10D4,",
+            "\u03A4\u03B7 \u03B3\u03BB\u03CE\u03C3\u03C3\u03B1 \u03BC\u03BF\u03C5 \u03AD\u03B4\u03C9\u03C3\u03B1\u03BD \u03B5\u03BB\u03BB\u03B7\u03BD\u03B9\u03BA\u03AE",
+            null,
+        };
+
+        public static IEnumerable<object[]> Utf8StringsWithIndex()
         {
-            throw new Exception("TestStringPassByOut : string mismatch");
+            for (int i = 0; i < Utf8Strings.Length; i++)
+                yield return [Utf8Strings[i], i];
         }
-    }
 
-    public static void EmptyStringTest()
-    {
-        StringParameterInOut(string.Empty, 0);
-        StringParameterOut(string.Empty, 0);
-    }
-}
-
-// UTF8 stringbuilder
-class UTF8StringBuilderTests
-{
-    [DllImport("UTF8TestNative", CallingConvention = CallingConvention.Cdecl)]
-    public static extern void StringBuilderParameterInOut([In, Out][MarshalAs(UnmanagedType.LPUTF8Str)]StringBuilder s, int index);
-    public static void TestInOutStringBuilderParameter(string expectedString, int index)
-    {
-        StringBuilder nativeStrBuilder = new StringBuilder(expectedString);
-        StringBuilderParameterInOut(nativeStrBuilder, index);
-
-        if (!nativeStrBuilder.ToString().Equals(expectedString))
+        public static IEnumerable<object[]> NonNullUtf8StringsWithIndex()
         {
-            throw new Exception("TestInOutStringBuilderParameter: nativeString != expectedNativeString ");
+            for (int i = 0; i < Utf8Strings.Length - 1; i++)
+                yield return [Utf8Strings[i], i];
         }
-    }
 
-    [DllImport("UTF8TestNative", CallingConvention = CallingConvention.Cdecl)]
-    public static extern void StringBuilderParameterOut([Out][MarshalAs(UnmanagedType.LPUTF8Str)]StringBuilder s, int index);
-    public static void TestOutStringBuilderParameter(string expectedString, int index)
-    {
-        // string builder capacity
-        StringBuilder nativeStringBuilder = new StringBuilder(expectedString.Length);
-        StringBuilderParameterOut(nativeStringBuilder, index);
-
-        if (!nativeStringBuilder.ToString().Equals(expectedString))
+        [Theory]
+        [MemberData(nameof(Utf8StringsWithIndex))]
+        public static void TestInOutStringParameter(string orgString, int index)
         {
-            throw new Exception("TestOutStringBuilderParameter: string != expectedString ");
+            string nativeString = StringParameterInOut(orgString, index);
+            Assert.Equal(orgString, nativeString);
         }
-    }
 
-
-    [DllImport("UTF8TestNative", CallingConvention = CallingConvention.Cdecl)]
-    [return: MarshalAs(UnmanagedType.LPUTF8Str,SizeConst = 512)]
-    public static extern StringBuilder StringBuilderParameterReturn(int index);
-    public static void TestReturnStringBuilder(string expectedReturn, int index)
-    {
-        StringBuilder nativeString = StringBuilderParameterReturn(index);
-        if (!expectedReturn.Equals(nativeString.ToString()))
+        [Theory]
+        [MemberData(nameof(Utf8StringsWithIndex))]
+        public static void TestOutStringParameter(string orgString, int index)
         {
-            throw new Exception(string.Format( "TestReturnStringBuilder: nativeString {0} != expectedNativeString {1}",nativeString.ToString(),expectedReturn) );
+            string nativeString = StringParameterOut(orgString, index);
+            Assert.Equal(orgString, nativeString);
         }
-    }
-}
-
-// UTF8 string as struct field
-class UTF8StructMarshalling
-{
-    public struct Utf8Struct
-    {
-        [MarshalAs(UnmanagedType.LPUTF8Str)]
-        public string FirstName;
-        public int index;
-    }
-
-    unsafe struct UnmanagedStruct
-    {
-      public fixed byte psz[8];
-    }
-
-    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
-    struct ManagedStruct
-    {
-      [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 8)]
-      public string str;
-    }
-
-    [DllImport("UTF8TestNative", CallingConvention = CallingConvention.Cdecl)]
-    public static extern void TestStructWithUtf8Field(Utf8Struct utfStruct);
-
-    [DllImport("UTF8TestNative", CallingConvention = CallingConvention.Cdecl)]
-    public static extern void SetStringInStruct(ref Utf8Struct utfStruct, [MarshalAs(UnmanagedType.LPUTF8Str)] string str);
 
-    public static void TestUTF8StructMarshalling(string[] utf8Strings)
-    {
-        Utf8Struct utf8Struct = new Utf8Struct();
-        for (int i = 0; i < utf8Strings.Length; i++)
+        [Theory]
+        [MemberData(nameof(NonNullUtf8StringsWithIndex))]
+        public static void TestStringPassByOut(string orgString, int index)
         {
-            utf8Struct.FirstName = utf8Strings[i];
-            utf8Struct.index = i;
-            TestStructWithUtf8Field(utf8Struct);
+            StringParameterRefOut(out string result, index);
+            Assert.Equal(orgString, result);
         }
-        if (!OperatingSystem.IsWindows())
-         CompareWithUTF8Encoding();
-
-        string testString = "StructTestString\uD83D\uDE00";
-
-        SetStringInStruct(ref utf8Struct, testString);
 
-        if (utf8Struct.FirstName != testString)
+        [Theory]
+        [MemberData(nameof(NonNullUtf8StringsWithIndex))]
+        public static void TestStringPassByRef(string orgString, int index)
         {
-            throw new Exception("Incorrect UTF8 string marshalled back from native to managed.");
+            string copy = new string(orgString.ToCharArray());
+            Assert.True(StringParameterRef(ref orgString, index));
+            Assert.Equal(copy, orgString);
         }
-   }
-
-   unsafe static void CompareWithUTF8Encoding()
-   {
-       // Compare results with UTF8Encoding
-        UnmanagedStruct ums;
-        ums.psz[0] = 0xFF;
-        ums.psz[1] = (byte)'a';
-        ums.psz[2] = (byte)'b';
-        ums.psz[3] = (byte)'c';
-        ums.psz[4] = (byte)'d';
-        ums.psz[5] = 0;
-
-        IntPtr ptr = (IntPtr)(&ums);
-        ManagedStruct ms = Marshal.PtrToStructure<ManagedStruct>(ptr);
-	string actual = ms.str;
-
-        UTF8Encoding uTF8Encoding = new UTF8Encoding();
-        byte [] b = new byte[5];
-        b[0] = 0xFF;
-        b[1] = (byte)'a';
-        b[2] = (byte)'b';
-        b[3] = (byte)'c';
-        b[4] = (byte)'d';
-        string expected = uTF8Encoding.GetString(b);
-        if (actual != expected)
-	{
-           Console.WriteLine("Actual:" + actual + " Length:" + actual.Length);
-           Console.WriteLine("Expected:" + expected + " Length:" + expected.Length);
-           throw new Exception("UTF8Encoding.GetString doesn't match with Utf8 String Marshaller result");
-        }
-   }
-}
 
-// UTF8 string as delegate parameter
-class UTF8DelegateMarshalling
-{
-    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
-    public delegate void DelegateUTF8Parameter([MarshalAs(UnmanagedType.LPUTF8Str)]string utf8String, int index);
-
-
-    [DllImport("UTF8TestNative", CallingConvention = CallingConvention.Cdecl)]
-    public static extern void Utf8DelegateAsParameter(DelegateUTF8Parameter param);
-
-
-    public static void TestUTF8DelegateMarshalling()
-    {
-        Utf8DelegateAsParameter(new DelegateUTF8Parameter(Utf8StringCallback));
-    }
-
-    public static void Utf8StringCallback(string nativeString, int index)
-    {
-        if (string.CompareOrdinal(nativeString, Test.utf8Strings[index]) != 0)
+        [Theory]
+        [MemberData(nameof(NonNullUtf8StringsWithIndex))]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/123529", typeof(TestLibrary.Utilities), nameof(TestLibrary.Utilities.IsNativeAot))]
+        public static void TestInOutStringBuilderParameter(string expectedString, int index)
         {
-            throw new Exception("Utf8StringCallback string do not match");
+            var builder = new StringBuilder(expectedString);
+            Assert.True(StringBuilderParameterInOut(builder, index));
+            Assert.Equal(expectedString, builder.ToString());
         }
-    }
-}
-
-
-public class Test
-{
-    //test strings
-    public static string[] utf8Strings = {
-                                "Managed",
-                                 "S\u00EEne kl\u00E2wen durh die wolken sint geslagen" ,
-                                 "\u0915\u093E\u091A\u0902 \u0936\u0915\u094D\u0928\u094B\u092E\u094D\u092F\u0924\u094D\u0924\u0941\u092E\u094D \u0964 \u0928\u094B\u092A\u0939\u093F\u0928\u0938\u094D\u0924\u093F \u092E\u093E\u092E\u094D",
-                                 "\u6211\u80FD\u541E\u4E0B\u73BB\u7483\u800C\u4E0D\u4F24\u8EAB\u4F53",
-                                 "\u10E6\u10DB\u10D4\u10E0\u10D7\u10E1\u10D8 \u10E8\u10D4\u10DB\u10D5\u10D4\u10D3\u10E0\u10D4,\u10E8\u10D4\u10DB\u10D5\u10D4\u10D3\u10E0\u10D4, \u10DC\u10E3\u10D7\u10E3 \u10D9\u10D5\u10DA\u10D0 \u10D3\u10D0\u10DB\u10EE\u10E1\u10DC\u10D0\u10E1 \u10E8\u10D4\u10DB\u10D5\u10D4\u10D3\u10E0\u10D4,\u10E1\u10DD\u10E4\u10DA\u10D8\u10E1\u10D0 \u10E8\u10D4\u10DB\u10D5\u10D4\u10D3\u10E0\u10D4, \u10E8\u10D4\u10DB\u10D5\u10D4\u10D3\u10E0\u10D4,\u10E8\u10D4\u10DB\u10D5\u10D4\u10D3\u10E0\u10D4,\u10E8\u10D4\u10DB\u10D5\u10D4\u10D3\u10E0\u10D4,\u10E8\u10E0\u10DD\u10DB\u10D0\u10E1\u10D0, \u10EA\u10D4\u10EA\u10EE\u10DA\u10E1, \u10EC\u10E7\u10D0\u10DA\u10E1\u10D0 \u10D3\u10D0 \u10DB\u10D8\u10EC\u10D0\u10E1\u10D0, \u10F0\u10D0\u10D4\u10E0\u10D7\u10D0 \u10D7\u10D0\u10DC\u10D0 \u10DB\u10E0\u10DD\u10DB\u10D0\u10E1\u10D0; \u10DB\u10DD\u10DB\u10EA\u10DC\u10D4\u10E1 \u10E4\u10E0\u10D7\u10D4\u10DC\u10D8 \u10D3\u10D0 \u10D0\u10E6\u10D5\u10E4\u10E0\u10D8\u10DC\u10D3\u10D4, \u10DB\u10D8\u10D5\u10F0\u10EE\u10D5\u10D3\u10D4 \u10DB\u10D0\u10E1 \u10E9\u10D4\u10DB\u10E1\u10D0 \u10DC\u10D3\u10DD\u10DB\u10D0\u10E1\u10D0, \u10D3\u10E6\u10D8\u10E1\u10D8\u10D7 \u10D3\u10D0 \u10E6\u10D0\u10DB\u10D8\u10D7 \u10D5\u10F0\u10EE\u10D4\u10D3\u10D5\u10D8\u10D3\u10D4 \u10DB\u10D6\u10D8\u10E1\u10D0 \u10D4\u10DA\u10D5\u10D0\u10D7\u10D0 \u10D9\u10E0\u10D7\u10DD\u10DB\u10D0\u10D0\u10E1\u10D0\u10E8\u10D4\u10DB\u10D5\u10D4\u10D3\u10E0\u10D4,\u10E8\u10D4\u10DB\u10D5\u10D4\u10D3\u10E0\u10D4,",
-                                 "\u03A4\u03B7 \u03B3\u03BB\u03CE\u03C3\u03C3\u03B1 \u03BC\u03BF\u03C5 \u03AD\u03B4\u03C9\u03C3\u03B1\u03BD \u03B5\u03BB\u03BB\u03B7\u03BD\u03B9\u03BA\u03AE",
-                                 null,
-                               };
-
-    [Fact]
-    [OuterLoop]
-    [ActiveIssue("https://github.com/dotnet/runtime/issues/91388", typeof(TestLibrary.PlatformDetection), nameof(TestLibrary.PlatformDetection.PlatformDoesNotSupportNativeTestAssets))]
-    public static void TestEntryPoint()
-    {
-        // Test string as [In,Out] parameter
-        for (int i = 0; i < utf8Strings.Length; i++)
-            UTF8StringTests.TestInOutStringParameter(utf8Strings[i], i);
-
-        // Test string as [Out] parameter
-        for (int i = 0; i < utf8Strings.Length; i++)
-            UTF8StringTests.TestOutStringParameter(utf8Strings[i], i);
 
-        for (int i = 0; i < utf8Strings.Length - 1; i++)
-            UTF8StringTests.TestStringPassByOut(utf8Strings[i], i);
+        [Theory]
+        [MemberData(nameof(NonNullUtf8StringsWithIndex))]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/123529", typeof(TestLibrary.Utilities), nameof(TestLibrary.Utilities.IsNativeAot))]
+        public static void TestOutStringBuilderParameter(string expectedString, int index)
+        {
+            var builder = new StringBuilder(expectedString.Length);
+            StringBuilderParameterOut(builder, index);
+            Assert.Equal(expectedString, builder.ToString());
+        }
 
-        for (int i = 0; i < utf8Strings.Length - 1; i++)
-            UTF8StringTests.TestStringPassByRef(utf8Strings[i], i);
+        [Theory]
+        [MemberData(nameof(NonNullUtf8StringsWithIndex))]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/123529", typeof(TestLibrary.Utilities), nameof(TestLibrary.Utilities.IsNativeAot))]
+        public static void TestReturnStringBuilder(string expectedReturn, int index)
+        {
+            StringBuilder nativeString = StringBuilderParameterReturn(index);
+            Assert.Equal(expectedReturn, nativeString.ToString());
+        }
 
-        // https://github.com/dotnet/runtime/issues/123529
-        if (!TestLibrary.Utilities.IsNativeAot)
+        [Theory]
+        [MemberData(nameof(Utf8StringsWithIndex))]
+        public static void TestStructWithUtf8FieldParameter(string str, int index)
         {
-            // Test StringBuilder as [In,Out] parameter
-            for (int i = 0; i < utf8Strings.Length - 1; i++)
-                UTF8StringBuilderTests.TestInOutStringBuilderParameter(utf8Strings[i], i);
+            var utf8Struct = new Utf8Struct { FirstName = str, index = index };
+            Assert.True(TestStructWithUtf8Field(utf8Struct));
+        }
 
-            // Test StringBuilder as [Out] parameter
-            for (int i = 0; i < utf8Strings.Length - 1; i++)
-                UTF8StringBuilderTests.TestOutStringBuilderParameter(utf8Strings[i], i);
+        [Fact]
+        public static void TestSetStringInStruct()
+        {
+            var utf8Struct = new Utf8Struct();
+            string testString = "StructTestString\uD83D\uDE00";
+            SetStringInStruct(ref utf8Struct, testString);
+            Assert.Equal(testString, utf8Struct.FirstName);
         }
 
-        // utf8 string as struct fields
-        UTF8StructMarshalling.TestUTF8StructMarshalling(utf8Strings);
+        [Fact]
+        public static void TestUTF8DelegateMarshalling()
+        {
+            Utf8DelegateAsParameter(new DelegateUTF8Parameter(Utf8StringCallback));
+        }
 
-        // delegate
-        UTF8DelegateMarshalling.TestUTF8DelegateMarshalling();
+        [Fact]
+        public static void TestEmptyString()
+        {
+            Assert.Null(StringParameterInOut(string.Empty, 0));
+            Assert.Null(StringParameterOut(string.Empty, 0));
+        }
 
-        // https://github.com/dotnet/runtime/issues/123529
-        if (!TestLibrary.Utilities.IsNativeAot)
+        [Fact]
+        public static unsafe void CompareWithUTF8Encoding()
         {
-            // Test StringBuilder as [Out] parameter
-            for (int i = 0; i < utf8Strings.Length - 1; i++)
-                UTF8StringBuilderTests.TestReturnStringBuilder(utf8Strings[i], i);
+            if (OperatingSystem.IsWindows())
+                return;
+
+            UnmanagedStruct ums;
+            ums.psz[0] = 0xFF;
+            ums.psz[1] = (byte)'a';
+            ums.psz[2] = (byte)'b';
+            ums.psz[3] = (byte)'c';
+            ums.psz[4] = (byte)'d';
+            ums.psz[5] = 0;
+
+            IntPtr ptr = (IntPtr)(&ums);
+            ManagedStruct ms = Marshal.PtrToStructure<ManagedStruct>(ptr);
+            string actual = ms.str;
+
+            UTF8Encoding uTF8Encoding = new UTF8Encoding();
+            byte[] b = new byte[5];
+            b[0] = 0xFF;
+            b[1] = (byte)'a';
+            b[2] = (byte)'b';
+            b[3] = (byte)'c';
+            b[4] = (byte)'d';
+            string expected = uTF8Encoding.GetString(b);
+            Assert.Equal(expected, actual);
         }
 
-        // String.Empty tests
-        UTF8StringTests.EmptyStringTest();
+        static void Utf8StringCallback(string nativeString, int index)
+        {
+            Assert.Equal(0, string.CompareOrdinal(nativeString, Utf8Strings[index]));
+        }
     }
 }
diff --git a/src/tests/Interop/StringMarshalling/UTF8/UTF8TestNative.cpp b/src/tests/Interop/StringMarshalling/UTF8/UTF8TestNative.cpp
index 11eb92075b7c24..0a535eba7138b4 100644
--- a/src/tests/Interop/StringMarshalling/UTF8/UTF8TestNative.cpp
+++ b/src/tests/Interop/StringMarshalling/UTF8/UTF8TestNative.cpp
@@ -43,7 +43,8 @@ char* utf16_to_utf8(const wchar_t *srcstring)
 
     if (!nc)
     {
-        throw;
+        CoreClrFree(pszUTF8);
+        return nullptr;
     }
 
     pszUTF8[nc] = '\0';
@@ -81,9 +82,9 @@ wchar_t* utf8_to_utf16(const char *utf8)
 
     if (!nc)
     {
-        throw;
+        CoreClrFree(wszTextUTF16);
+        return nullptr;
     }
-    //MultiByteToWideChar do not null terminate the string when cbMultiByte is not -1
     wszTextUTF16[nc] = '\0';
     return wszTextUTF16;
 }
@@ -135,11 +136,11 @@ LPSTR build_return_string(const char* pReturn)
 }
 
 // Modify the string builder in place, managed side validates.
-extern "C" DLL_EXPORT void __cdecl StringBuilderParameterInOut(/*[In,Out] StringBuilder*/ char *s, int index)
+extern "C" DLL_EXPORT BOOL __cdecl StringBuilderParameterInOut(/*[In,Out] StringBuilder*/ char *s, int index)
 {
     // if string.empty
     if (s == 0 || *s == 0)
-        return;
+        return TRUE;
 
     char *pszTextutf8 = get_utf8_string(index);
 
@@ -150,7 +151,8 @@ extern "C" DLL_EXPORT void __cdecl StringBuilderParameterInOut(/*[In,Out] String
         if (s[i] != pszTextutf8[i])
         {
             printf("[in] managed string do not match native string\n");
-            throw;
+            free_utf8_string(pszTextutf8);
+            return FALSE;
         }
     }
 
@@ -161,6 +163,7 @@ extern "C" DLL_EXPORT void __cdecl StringBuilderParameterInOut(/*[In,Out] String
     }
     s[outLen] = '\0';
     free_utf8_string(pszTextutf8);
+    return TRUE;
 }
 
 //out string builder
@@ -209,7 +212,7 @@ typedef struct FieldWithUtf8
 }FieldWithUtf8;
 
 //utf8 struct field
-extern "C" DLL_EXPORT void __cdecl TestStructWithUtf8Field(struct FieldWithUtf8 fieldStruct)
+extern "C" DLL_EXPORT BOOL __cdecl TestStructWithUtf8Field(struct FieldWithUtf8 fieldStruct)
 {
     char *pszManagedutf8 = fieldStruct.pFirst;
     int stringIndex = fieldStruct.index;
@@ -217,7 +220,7 @@ extern "C" DLL_EXPORT void __cdecl TestStructWithUtf8Field(struct FieldWithUtf8
     size_t outLen = 0;
 
     if (pszManagedutf8 == 0 || *pszManagedutf8 == 0)
-        return;
+        return TRUE;
 
     pszNative = get_utf8_string(stringIndex);
     outLen = strlen(pszNative);
@@ -227,10 +230,12 @@ extern "C" DLL_EXPORT void __cdecl TestStructWithUtf8Field(struct FieldWithUtf8
         if (pszNative[i] != pszManagedutf8[i])
         {
             printf("Native and managed string do not match.\n");
-            throw;
+            free_utf8_string(pszNative);
+            return FALSE;
         }
     }
     free_utf8_string(pszNative);
+    return TRUE;
 }
 
 extern "C" DLL_EXPORT void __cdecl SetStringInStruct(FieldWithUtf8* fieldStruct, char* str)
@@ -255,7 +260,7 @@ extern "C" DLL_EXPORT void __cdecl StringParameterRefOut(/*out*/ char **s, int i
 }
 
 //c# ref
-extern "C" DLL_EXPORT void __cdecl StringParameterRef(/*ref*/ char **s, int index)
+extern "C" DLL_EXPORT BOOL __cdecl StringParameterRef(/*ref*/ char **s, int index)
 {
     char *pszTextutf8 = get_utf8_string(index);
     size_t strLength = strlen(pszTextutf8);
@@ -266,7 +271,8 @@ extern "C" DLL_EXPORT void __cdecl StringParameterRef(/*ref*/ char **s, int inde
         if ((*s)[i] != pszTextutf8[i])
         {
             printf("[in] managed string do not match native string\n");
-            throw;
+            free_utf8_string(pszTextutf8);
+            return FALSE;
         }
     }
 
@@ -279,6 +285,7 @@ extern "C" DLL_EXPORT void __cdecl StringParameterRef(/*ref*/ char **s, int inde
     memcpy(*s, pszTextutf8, strLength);
     (*s)[strLength] = '\0';
     free_utf8_string(pszTextutf8);
+    return TRUE;
 }
 
 // delegate test