type TClass1 = class(TInterfacedObject);

       ITest = interface(IInterface)
         procedure Test;stdcall;
       End;

       TClass2 = class(TClass1, ITest)
         procedure Test;stdcall;
       End;
...
var Class1 : TClass1;
...
Class1 := TClass2.Create;

type ITest = interface
    procedure Test; stdcall;
  end;

  TClass2 = class (TInterfacedObject, ITest)
    procedure Test; stdcall;
  end;

type
  ITest = interface (IUnknown) ['{839980A6-CEF2-4FF4-B56B-8EA1C3C15CB8}']
   // Blubb
  end;

TPlugin = class(TMyInterfacedObject)
  private
    FName        : String;
    FAuthor      : String;
    FFinalizeLib : TFinalizeLib;
    FLibrary     : TLibHandle;
  public
    constructor Create(const ALibHandle : TLibHandle; AFinalizeLib : TFinalizeLib; const AName : String; const AAuthor : String);

    property FinalizeLib : TFinalizeLib read FFinalizeLib;
  published
    property Name      : String     read FName;
    property Author    : String     read FAuthor;
    property LibHandle : TLibHandle read FLibrary;
  end;

const SBVPlugin = '{8908E562-66CA-4A8D-906F-C7FCD07B7B10}';
IBVPlugin = Interface(IInterface)[SBVPlugin]
       function FindBV(ASNode : TSceneNode) : TBoundingVolume;
     End;

TDefPlugin = class(TPlugin, IBVPlugin)
     public
       function FindBV(ASNode : TSceneNode) : TBoundingVolume;
     End;   

var P : TPlugin;
...
P := TDefPlugin.Create;
BoundingV.Checked := Sysutils.Supports(P, StringToGUID(SBVPlugin));   // liefert false
...