At the core of the library is IFileSystem
and FileSystem
. Instead of calling methods like File.ReadAllText
directly, use IFileSystem.File.ReadAllText
. We have exactly the same API, except that ours is injectable and testable.
dotnet add package TestableIO.System.IO.Abstractions.Wrappers
Note: This NuGet package is also published as System.IO.Abstractions
but we suggest to use the prefix to make clear that this is not an official .NET package.
public class MyComponent
{
readonly IFileSystem fileSystem;
// <summary>Create MyComponent with the given fileSystem implementation</summary>
public MyComponent(IFileSystem fileSystem)
{
this.fileSystem = fileSystem;
}
/// <summary>Create MyComponent</summary>
public MyComponent() : this(
fileSystem: new FileSystem() //use default implementation which calls System.IO
)
{
}
public void Validate()
{
foreach (var textFile in fileSystem.Directory.GetFiles(@"c:\", "*.txt", SearchOption.TopDirectoryOnly))
{
var text = fileSystem.File.ReadAllText(textFile);
if (text != "Testing is awesome.")
throw new NotSupportedException("We can't go on together. It's not me, it's you.");
}
}
}
The library also ships with a series of test helpers to save you from having to mock out every call, for basic scenarios. They are not a complete copy of a real-life file system, but they'll get you most of the way there.
dotnet add package TestableIO.System.IO.Abstractions.TestingHelpers
Note: This NuGet package is also published as System.IO.Abstractions.TestingHelpers
but we suggest to use the prefix to make clear that this is not an official .NET package.
[Test]
public void MyComponent_Validate_ShouldThrowNotSupportedExceptionIfTestingIsNotAwesome()
{
// Arrange
var fileSystem = new MockFileSystem(new Dictionary<string, MockFileData>
{
{ @"c:\myfile.txt", new MockFileData("Testing is meh.") },
{ @"c:\demo\jQuery.js", new MockFileData("some js") },
{ @"c:\demo\image.gif", new MockFileData(new byte[] { 0x12, 0x34, 0x56, 0xd2 }) }
});
var component = new MyComponent(fileSystem);
try
{
// Act
component.Validate();
}
catch (NotSupportedException ex)
{
// Assert
Assert.AreEqual("We can't go on together. It's not me, it's you.", ex.Message);
return;
}
Assert.Fail("The expected exception was not thrown.");
}
We even support casting from the .NET Framework's untestable types to our testable wrappers:
FileInfo SomeApiMethodThatReturnsFileInfo()
{
return new FileInfo("a");
}
void MyFancyMethod()
{
var testableFileInfo = (FileInfoBase)SomeApiMethodThatReturnsFileInfo();
...
}
Since version 4.0 the top-level APIs expose interfaces instead of abstract base classes (these still exist, though), allowing you to completely mock the file system. Here's a small example, using Moq:
[Test]
public void Test1()
{
var watcher = Mock.Of<IFileSystemWatcher>();
var file = Mock.Of<IFile>();
Mock.Get(file).Setup(f => f.Exists(It.IsAny<string>())).Returns(true);
Mock.Get(file).Setup(f => f.ReadAllText(It.IsAny<string>())).Throws<OutOfMemoryException>();
var unitUnderTest = new SomeClassUsingFileSystemWatcher(watcher, file);
Assert.Throws<OutOfMemoryException>(() => {
Mock.Get(watcher).Raise(w => w.Created += null, new System.IO.FileSystemEventArgs(System.IO.WatcherChangeTypes.Created, @"C:\Some\Directory", "Some.File"));
});
Mock.Get(file).Verify(f => f.Exists(It.IsAny<string>()), Times.Once);
Assert.True(unitUnderTest.FileWasCreated);
}
public class SomeClassUsingFileSystemWatcher
{
private readonly IFileSystemWatcher _watcher;
private readonly IFile _file;
public bool FileWasCreated { get; private set; }
public SomeClassUsingFileSystemWatcher(IFileSystemWatcher watcher, IFile file)
{
this._file = file;
this._watcher = watcher;
this._watcher.Created += Watcher_Created;
}
private void Watcher_Created(object sender, System.IO.FileSystemEventArgs e)
{
FileWasCreated = true;
if(_file.Exists(e.FullPath))
{
var text = _file.ReadAllText(e.FullPath);
}
}
}
-
System.IO.Abstractions.Extensions
provides convenience functionality on top of the core abstractions. -
System.IO.Abstractions.Analyzers
provides Roslyn analyzers to help use abstractions over static methods. -
Testably.Abstractions
provides alternative test helpers and additional abstractions.