chore: import upstream snapshot with attribution

tests/fixtures/Sample.cs

@@ -0,0 +1,48 @@
+using System;
+using System.Collections.Generic;
+
+namespace SampleApp
+{
+    public interface IRepository
+    {
+        User FindById(int id);
+        void Save(User user);
+    }
+
+    public class User
+    {
+        public int Id { get; set; }
+        public string Name { get; set; }
+    }
+
+    public class InMemoryRepo : IRepository
+    {
+        private Dictionary<int, User> _users = new();
+
+        public User FindById(int id)
+        {
+            return _users.ContainsKey(id) ? _users[id] : null;
+        }
+
+        public void Save(User user)
+        {
+            _users[user.Id] = user;
+            Console.WriteLine($"Saved user {user.Id}");
+        }
+    }
+
+    public class UserService
+    {
+        private IRepository _repo;
+
+        public UserService(IRepository repo)
+        {
+            _repo = repo;
+        }
+
+        public User GetUser(int id)
+        {
+            return _repo.FindById(id);
+        }
+    }
+}