problems with LayerTabBar in unit tests

Hi all,

I'm still working on a unit test for bug tdf#119956. My current state 
is, that the odg test document really opens in Draw. [On master it opens 
in Impress.] But the layer tab bar has width 0. So simulating a click on 
the layer tab bar is not possible, which is needed in case of bug 
tdf#119956.

Which layers are shown in the layer tab bar is calculated in 
DrawViewShell::ResetActualLayer() in sd/source/ui/view/drviews1.cxx and 
the actual width is calculated in TabBar::ImplFormat() in 
svtools/source/control/tabbar.cxx. Please correct me, if I'm wrong about 
this.

So my questions are:

What makes the method SdMiscTest::Load from misc-tests.cxx in sd/qa/unit 
different from regular opening the file from a running LibreOffice via 
click on Open button of the start center?

How can I open the test file in a unit test the same way as a regular 
Open does?

Or what do I need to add/change in the SdMiscTest::Load method to get 
the layer tab bar in the correct width?

Any ideas or tips?

Kind regards
Regina