using System;
using System.Linq;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Data.Sqlite;
using Microsoft.EntityFrameworkCore;

await using var connection = new SqliteConnection("Data Source=:memory:;Foreign Keys=True");
await connection.OpenAsync();
var options = new DbContextOptionsBuilder<LabDb>().UseSqlite(connection).Options;
await using (var db = new LabDb(options)) { await db.Database.EnsureCreatedAsync(); db.Items.Add(new Item { Name = "Original", Sku = "R1" }); await db.SaveChangesAsync(); }
bool duplicate = false;
await using (var db = new LabDb(options))
{
    db.Items.Add(new Item { Name = "Duplicate", Sku = "R1" });
    try { await db.SaveChangesAsync(); }
    catch (DbUpdateException ex) when (ex.InnerException is SqliteException { SqliteErrorCode: 19, SqliteExtendedErrorCode: 2067 }) { duplicate = true; }
}
await using (var verify = new LabDb(options)) { Check(duplicate && await verify.Items.CountAsync() == 1 && (await verify.Items.SingleAsync()).Name == "Original", "unique index preserves original"); }
Console.WriteLine("unique:rejected"); Console.WriteLine("rows:1");

static void Check(bool condition, string name) { if (!condition) throw new InvalidOperationException("CHECK: " + name); }