This library is an alternative testing helper for the IFileSystem interfaces from System.IO.Abstractions. These interfaces allow abstracting away all I/O-related functionality from the System.IO namespace.
In addition, the following interfaces are defined:

• The ITimeSystem interface abstracts away time-related functionality:
  DateTime methods give access to the current time, Thread allows replacing Thread.Sleep and Task allows replacing Task.Delay.
• The IRandomSystem interface abstracts away functionality related to randomness:
  Random methods implement a thread-safe Shared instance also under .NET Framework and Guid methods allow creating new GUIDs.

Use the interfaces and their default implementations using your prefered dependency injection method, e.g.:

private readonly IFileSystem _fileSystem;

public class MyService(IFileSystem fileSystem)
{
    _fileSystem = fileSystem;
}

public void StoreData()
{
    var fileContent = GetFileContent();
    _fileSystem.File.WriteAllText("result.xml", fileContent);
}

private string GetFileContent()
{
    // Generate the file content
}

Then you test your class with the mocked types in Testably.Abstractions.Testing:

[Fact]
public void StoreData_ShouldWriteValidFile()
{
    IFileSystem fileSystem = new MockFileSystem();
    MyService sut = new MyService(fileSystem);

    sut.StoreData();

    var fileContent = fileSystem.File.ReadAllText("result.xml");
    // Validate fileContent
}

More examples can be found in the examples section!

• Install Testably.Abstractions as nuget package in your productive projects and Testably.Abstractions.Testing as nuget package in your test projects.

  dotnet add package Testably.Abstractions
  dotnet add package Testably.Abstractions.Testing

• Configure your dependeny injection framework, e.g. with Microsoft.Extensions.DependencyInjections in ASP.NET core:

  builder.Services
      .AddSingleton<IFileSystem, RealFileSystem>()
      .AddSingleton<IRandomSystem, RealRandomSystem>()
      .AddSingleton<ITimeSystem, RealTimeSystem>();

You can now use the interfaces in your services!

In order to simplify testing, the Testably.Abstractions.Testing projects provides mocked instances for the abstraction interfaces:

These mocks are configured using fluent syntax:

new MockFileSystem()
    .WithDrive("D:", d => d
        .SetTotalSize(1024*1024))
    .Initialize()
        .WithAFile()
        .WithASubdirectory().Initialized(s => s
            .WithAFile(".txt"));

Initializes the mocked file system with a second drive D: with 1MB total available space and creates on the default drive C: a random file and a random sub-directory containing a ".txt" file.