public void File_AppendText()
{
const string contents = "test";
var fn = GetNewFileNameOnTempPath(".txt");
Assert.IsFalse(System.IO.File.Exists(fn));
FileSystem.AppendText(fn, contents);
Assert.IsTrue(System.IO.File.Exists(fn));
FileSystem.AppendText(fn, contents);
Assert.AreEqual(contents + contents, System.IO.File.ReadAllText(fn));
}