Testably.Abstractions

Testably.Abstractions is a feature-complete testing helper for the IFileSystem abstractions of the System.IO namespace, plus matching abstractions for time and randomness.

It provides:

• An in-memory MockFileSystem that behaves exactly like the real file system. The whole test suite runs against both implementations, so the mock and reality stay in sync.
• An ITimeSystem abstraction for DateTime, Stopwatch, Task.Delay, Thread.Sleep, PeriodicTimer and Timer.
• An IRandomSystem abstraction for Random (with a thread-safe Shared instance also under .NET Framework) and Guid.
• Companion packages Testably.Abstractions.Compression (Zip files) and Testably.Abstractions.AccessControl (ACLs).

Why another file system mock?

Testably.Abstractions shares the IFileSystem interface with TestableIO.System.IO.Abstractions - your production code does not change when you switch testing libraries. What you get on top:

• Advanced testing scenarios: FileSystemWatcher, SafeFileHandle, multiple drives with size limits.
• Cross-platform simulation: run a Linux file system on Windows (and vice versa) to exercise platform-specific behaviour from a single CI job.
• A second abstraction layer for time and randomness.

See Migration from TestableIO if you are already using TestableIO.

A short example

public class MyService(IFileSystem fileSystem)
{
    private readonly IFileSystem _fileSystem = fileSystem;

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

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

    sut.StoreData();

    var content = fileSystem.File.ReadAllText("result.xml");
    // assert on content
}

Continue with Getting Started to install the packages and wire them up, then explore File system, Time system, Random system and the Companion libraries.