Program.cs

usingMicrosoft.Extensions.Hosting.WindowsServices;

// https://stackoverflow.com/questions/69909593/asp-net-6-custom-webapplicationfactory-throws-exception
varoptions=newWebApplicationOptions
{
Args=args,
ContentRootPath=WindowsServiceHelpers.IsWindowsService()?AppContext.BaseDirectory:default,
WebRootPath="wwwroot",
ApplicationName=typeof(Program).Assembly.FullName
};

varbuilder=WebApplication.CreateBuilder(options);
builder.Host.UseWindowsService();
builder.WebHost.UseUrls("http://localhost:5300");
varapp=builder.Build();

app.Run(async context =>
{
awaitcontext.Response.WriteAsync($"This is hello world running from a Windows Service");
});

app.Run();