MiniExcel/tests/MiniExcel.Tests.AspNetCore/Startup.cs

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.DependencyInjection;
using System.IO;
using MiniExcelLibs;

public class Startup
{
    public void ConfigureServices(IServiceCollection services) => services.AddMvc();
    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        app.UseRouting();
        app.UseEndpoints(endpoints => endpoints.MapDefaultControllerRoute());
    }
}
public class HomeController : Controller
{
    public IActionResult Index()
    {
        var values = new[] {
            new { Column1 = "MiniExcel", Column2 = 1 },
            new { Column1 = "Github", Column2 = 2}
        };
        var stream = new MemoryStream();
        stream.SaveAs(values);
        return File(stream,
            "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
            "demo.xlsx");
    }
}