//在.Net Core中，读取配对文件是通过IConfiguration接口操作的，实例化接口对象如下所示：

Program.cs中配置如下：

//引用Microsoft.Extensions.Configuration;

var Configuration = new ConfigurationBuilder()
.SetBasePath(System.IO.Directory.GetCurrentDirectory())
.AddJsonFile("appsettings.json")
.AddJsonFile("appsettings.test.json", true, reloadOnChange: true).Build();

或者如下：

IConfiguration Configuration = new ConfigurationBuilder()
.SetBasePath(System.IO.Directory.GetCurrentDirectory())
.AddJsonFile("appsettings.json")
.AddJsonFile("appsettings.test.json", true, reloadOnChange: true).Build();

Console.WriteLine($"Logging:{Configuration["Logging:LogLevel:Default"]}");  //测试读取