Add csc.rsp & test project for unity

src/Utf8StringInterpolation.Unity/Assets/Tests/Utf8StringInterpolation.Tests.asmdef

@@ -0,0 +1,22 @@
+{
+    "name": "Utf8StringInterpolation.Tests",
+    "rootNamespace": "",
+    "references": [
+        "UnityEngine.TestRunner",
+        "UnityEditor.TestRunner",
+        "Utf8StringInterpolation"
+    ],
+    "includePlatforms": [],
+    "excludePlatforms": [],
+    "allowUnsafeCode": false,
+    "overrideReferences": true,
+    "precompiledReferences": [
+        "nunit.framework.dll"
+    ],
+    "autoReferenced": false,
+    "defineConstraints": [
+        "UNITY_INCLUDE_TESTS"
+    ],
+    "versionDefines": [],
+    "noEngineReferences": false
+}

src/Utf8StringInterpolation.Unity/Assets/Tests/Utf8StringTest.cs

@@ -0,0 +1,21 @@
+using System.Collections;
+using System.Collections.Generic;
+using System.Text;
+using NUnit.Framework;
+using UnityEngine;
+
+
+namespace Utf8StringInterpolation.Tests;
+
+public class Utf8StringTest
+{
+    [Test]
+    public void Sample()
+    {
+        var name = "foo";
+        var id = 123;
+        var result = Utf8String.Format($"Hello, {name}, Your id is {id}!");
+        var expected = Encoding.UTF8.GetBytes($"Hello, {name}, Your id is {id}!");
+        Assert.That(result, Is.EquivalentTo(expected));
+    }
+}

src/Utf8StringInterpolation.Unity/ProjectSettings/ProjectSettings.asset

@@ -641,8 +641,7 @@ PlayerSettings:
   webGLPowerPreference: 2
   scriptingDefineSymbols: {}
   additionalCompilerArguments:
-    Standalone:
-    - -langVersion:latest
+    Standalone: []
   platformArchitecture: {}
   scriptingBackend: {}
   il2cppCompilerConfiguration: {}

src/Utf8StringInterpolation/Utf8String.cs

@@ -10,7 +10,7 @@ namespace Utf8StringInterpolation;
 public static class Utf8String
 {
     // Format API
-
+   
     public static byte[] Format(ref Utf8StringWriter<ArrayBufferWriter<byte>> format)
     {
         format.Flush();