using NuGet.Test.Mocks; using System.IO; public class MyFileReader { public string ReadFile(string path) { var fileSystem = new MockFileSystem(); fileSystem.AddFile(path, new MockFileData("Hello World")); return fileSystem.File.ReadAllText(path); } }In this example, we create a new instance of the `MockFileSystem` class and add a file with the contents "Hello World" to it. We then call the `ReadAllText` method on the file and return its contents. Package Library: NuGet.Test.Mocks