---
layout: post
title: Testing with a Temporary Directory
---
<p>When testing a class that interacts with the file system, it’s useful to have a clean “temp” directory. We don’t want old files lying around, which could randomly break later tests.</p>
<p>The System.IO.Path class has a static method GetTempPath. This returns the path of the system’s temporary folder. Rather than work directly in the temp directory, we can create a new, uniquely named, directory for each test. This makes cleaning up after the test easy – simply delete the directory.</p>
<p>This repeated pattern of using a temporary directory can be encapsulated into a simple class.</p>
<code><pre class="brush: csharp">class TempDirectory : IDisposable
{
    public TempDirectory()
    {
        path = Path.Combine(
            Path.GetTempPath(),
            Guid.NewGuid().ToString()
        );
        Directory.CreateDirectory(path);
    }

    readonly string path;

    /// <summary>
    /// Allows the TempDirectory to be used anywhere a string is required.
    /// </summary>
    public static implicit operator string(TempDirectory directory)
    {
        return directory.path;
    }

    public override string ToString()
    {
        return path;
    }

    public void Dispose()
    {
        Directory.Delete(path, true);
    }
}</pre></code>
<p>Here’s a simple test using the TempDirectory class:</p>
<code><pre class="brush: csharp">[Test]
public void SimpleTest()
{
    using (var temp = new TempDirectory())
    {
        // Temp directory is used as a string...
        File.WriteAllText(Path.Combine(temp, "file.txt"), "hello");
        var widget = new FileWidget(temp);
        widget.Load("file.txt");
        Assert.AreEqual("hello", widget.Title);
    }
}</pre></code>
<p>The TempDirectory creates a new, uniquely named, temporary directory. The class is disposable, so can be used in a using statement. This ensures the directory is deleted, even if the test code throws an unhandled exception.</p>
<p>The implicit cast to string operator allows us to use the TempDirectory as if it were a string. When passing it as a string argument, the full path to the directory is used.</p>
<p>This simple class could also be extended with methods that allow you to quickly set up temporary files as well.</p>
<p>P.S. Obviously it’s a good idea to avoid spreading file I/O throughout all your objects! However, there will always be some point where performing real I/O is appropriate. I hope this simple class proves useful for testing those objects.</p>