ddraw/tests: IDirect3DViewport3, IDirect3DViewport2 and IDirect3DViewport use same implementation.

dlls/ddraw/tests/d3d.c

@@ -1186,6 +1186,7 @@ static void ViewportTest(void)
 {
     HRESULT hr;
     LPDIRECT3DVIEWPORT2 Viewport2;
+    IDirect3DViewport3 *Viewport3;
     D3DVIEWPORT vp1_data, ret_vp1_data;
     D3DVIEWPORT2 vp2_data, ret_vp2_data;
     float infinity;
@@ -1197,6 +1198,12 @@ static void ViewportTest(void)
 
     hr = IDirect3DViewport_QueryInterface(Viewport, &IID_IDirect3DViewport2, (void**) &Viewport2);
     ok(hr==D3D_OK, "QueryInterface returned: %x\n", hr);
+    ok(Viewport2 == (IDirect3DViewport2 *)Viewport, "IDirect3DViewport2 iface diffrent from IDirect3DViewport\n");
+
+    hr = IDirect3DViewport_QueryInterface(Viewport, &IID_IDirect3DViewport3, (void**) &Viewport3);
+    ok(hr==D3D_OK, "QueryInterface returned: %x\n", hr);
+    ok(Viewport3 == (IDirect3DViewport3 *)Viewport, "IDirect3DViewport3 iface diffrent from IDirect3DViewport\n");
+    IDirect3DViewport3_Release(Viewport3);
 
     vp1_data.dwSize = sizeof(vp1_data);
     vp1_data.dwX = 0;