void CheckFile(FileSystemItem fileSystemItem, string filePath, out long fileSize)
{
Assert.IsTrue(fileSystemItem is FileItem);
Assert.AreEqual(Path.GetFileName(filePath), fileSystemItem.DisplayName);
Assert.AreEqual(filePath, fileSystemItem.GetPath());
FileInfo info = new FileInfo(filePath);
fileSize = info.Length;
Assert.AreEqual(fileSize, fileSystemItem.Size, filePath);
}