public void GetUniqueIdTest()
{
DocumentDataModel model = new DocumentDataModel();
model.New(new Size(700, 1200), new Thickness(32, 32, 32, 32));
DocumentDataModelInvariant(model);
Assert.AreEqual(DataModel.ModelState.Ready, model.State);
// The first unique id should be auto_0:
string firstUniqueId = model.GetUniqueId();
Assert.AreEqual("auto_0", firstUniqueId);
Assert.AreSame(null, model.GetShapeById(firstUniqueId));
// Adding an id which almost looks like an auto-id does not change GetUniqueId.
XElement shape = model.AddShape(new XElement("Test", new XAttribute("Id", "auto_not")));
Assert.AreEqual(firstUniqueId, model.GetUniqueId());
shape = model.AddShape(new XElement("Test", new XAttribute("Id", firstUniqueId)));
Assert.AreSame(shape, model.GetShapeById(firstUniqueId));
// The second unique id should be auto_1:
string secondUniqueId = model.GetUniqueId();
Assert.AreEqual("auto_1", secondUniqueId);
Assert.AreSame(null, model.GetShapeById(secondUniqueId));
// Removing a shape should not cause the unique id to decrement.
shape.Remove();
Assert.AreEqual(secondUniqueId, model.GetUniqueId());
DocumentDataModelInvariant(model);
Assert.AreEqual(DataModel.ModelState.Ready, model.State);
}