How do I write a unit test that relies on file system events?

Question

I have the following code that I'd like to test:

public class DirectoryProcessor
{
    public string DirectoryPath
    {
        get;
        set;
    }

    private FileSystemWatcher watcher;

    public event EventHandler<SourceEventArgs> SourceFileChanged;

    protected virtual void OnSourceFileChanged(SourceEventArgs e)
    {
        EventHandler<SourceEventArgs> handler = SourceFileChanged;
        if(handler != null)
        {
            handler(this, e);
        }
    }

    public DirectoryProcessor(string directoryPath)
    {
        this.DirectoryPath = directoryPath;
        this.watcher = new FileSystemWatcher(directoryPath);
        this.watcher.Created += new FileSystemEventHandler(Created);
    }

    void Created(object sender, FileSystemEventArgs e)
    {
        // process the newly created file
        // then raise my own event indicating that processing is done
        OnSourceFileChanged(new SourceEventArgs(e.Name));
    }
}

Basically, I want to write an NUnit test that will do the following:

1. Create a directory
2. Setup a DirectoryProcessor
3. Write some files to the directory (via File.WriteAllText())
4. Check that DirectoryProcessor.SourceFileChanged has fired once for each file added in step 3.

I tried doing this and adding Thread.Sleep() after step 3, but it's hard to get the timeout correct. It correctly processes the first file I write to the directory, but not the second (and that's with the timeout set to 60s). Even if I could get it working this way, it seems like a terrible way to write the test.

Does anyone have a good solution to this problem?

Answer 1

If you are looking to test another object that uses this class my answer is not relevant.

When I write unit tests to operations I prefer using the ManualResetEvent

The unit test will be something like:

     ...
     DirectoryProcessor.SourceFileChanged+=onChanged;
     manualResetEvent.Reset();
     File.WriteAllText();
     var actual = manualResetEvent.WaitOne(MaxTimeout);
     ...

when manualResetEvent is the ManualResetEvent and the MaxTimeout is some TimeSpan (my advice always use the time out). now we are missing the "onChanged":

     private void onChanged(object sender, SourceEventArgs e)
     {
          manualResetEvent.Set();
     }    

I hope this is helpful