单元测试中的 IConfiguration 怎么模拟？

.NET Core或者.Net 6 中我们可以配置文件来添加值（appsetting.json）,在写单元测试时我们怎么模拟这些值呢？比如以下一段代码：

[Fact]
public void Test_IsConfigured_Positive()
{

  // test against this configuration
  IConfiguration config = new ConfigurationBuilder()
    // how to populate it via code
    .Build();

  // the extension method to test
  Assert.True(config.IsConfigured());

}

在Builder完成后我想以这样的文件来构建

{
  "MySection": {
     // the existence of the section activates something triggering IsConfigured to be true but does not overwrite any default value
   }
 }

正确的答案是使用MemoryConfigurationBuilderExtensions  来做一个参数字典，代码如下：

using Microsoft.Extensions.Configuration;

var myConfiguration = new Dictionary<string, string>
{
    {"Key1", "Value1"},
    {"Nested:Key1", "NestedValue1"},
    {"Nested:Key2", "NestedValue2"}
};

var configuration = new ConfigurationBuilder()
    .AddInMemoryCollection(myConfiguration)
    .Build();

它的值映射成json文件格式如下：

{
  "Key1": "Value1",
  "Nested": {
    "Key1": "NestedValue1",
    "Key2": "NestedValue2"
  }
}

或者还有以下有价值的写法：

var configuration = new Mock<IConfiguration>();
var configSection = new Mock<IConfigurationSection>();

configSection.Setup(x => x.Value).Returns("fake value");
configuration.Setup(x => x.GetSection("MySection")).Returns(configSection.Object);
//OR
configuration.Setup(x => x.GetSection("MySection:Value")).Returns(configSection.Object);