FileSystemWatcher not working with Unit test

Question

i try this simple test to work with FileSystemWatcher Class but the OnFileChanged event not firing

    [Test]
    public void CanNotifyWhenFileChanged()
    {

        var watcher = new XMLWatcher(_path);
        watcher.StartWatching();
        AddXMLNodeTofile(_path);// change the file
        bool c = watcher.IsFileChanged;
        Assert.IsTrue(c);

    }

and this is my Method

public void StartWatching()
{
    var watcher = new FileSystemWatcher
                      {
                          Path =
                             Path.GetDirectoryName(System.Reflection.Assembly.GetExecutingAssembly().Location),
                          IncludeSubdirectories = false,
                          NotifyFilter = NotifyFilters.LastAccess |
                                         NotifyFilters.LastWrite |
                                         NotifyFilters.FileName |
                                         NotifyFilters.DirectoryName,
                          Filter = FilePath
                      };

    watcher.Changed += OnFileChanged;
    watcher.EnableRaisingEvents = true;

}

Answer 1

Please note that some Unit Test runners (NUnit, MSTest) do shadow copying of files i.e. the test binaries are copied to a separate location before execution. Hence the _path and the path where your test assembly reside may not be the same.

Also make sure that _path and the folder you are watching are the same.

Answer 2

Your test is probably completing before the event is fired. I use a library called FluentAssertions for testing events.