How to create Assembly

[Tejal-Alai]

I want to create assembly I tried it by 2 ways
1)I have tried to create ArrayList of ModelObjects and then tried to create assembly using Assembly.Add method but its throwing error.

        List<ModelObject> modelObjectsList = new List<ModelObject>();
        Beam beam = new Beam();
        ModelObject modelObject = beam as ModelObject;
        modelObjectsList.Add(modelObject);
        ArrayList arrayListofAssemblables = new ArrayList();
        arrayListofAssemblables.Add(modelObjectsList);
        Assembly assembly = new Assembly();
        assembly.Add(arrayListofAssemblables);

2. Passing model object to IAssemblable and then pass it to .Add method but its still throwing error that 'Assemblable is not valid'

        Beam beam = new Beam();
        ModelObject modelObject = beam as ModelObject;
        Assembly assembly = new Assembly();
        IAssemblable assemblable = modelObject as IAssemblable;
        assembly.Add(assemblable);
   

[CarlosHerrero]

Internal code of TeklaStructures creates assembly automatically when a part is inserted.
myPart.Insert();
myPart.GetAssembly(); // returns the assembly created by internal code

[Tejal-Alai]

myPart.Insert();
this is not working for me as i have to do unit testing of my function which takes assembly as input and while unit testing i can not insert functionality