HowTo load a file in unit test in xmloff?

Hi all,

I try to write a unit test in xmloff for 
https://gerrit.libreoffice.org/66888. I would need to load a file and 
examine, whether it is rendered correctly. My idea was to use 
loadFromDesktop() from unotest::MacrosTest. I have tried to mimic what I 
have seen elsewhere, but it does not work. What I have done so far:

class DrawTest : public test::BootstrapFixture, public unotest::MacrosTest

and then

void DrawTest::setUp()
{
    BootstrapFixture::setUp();

mxComponentContext.set(comphelper::getComponentContext(getMultiServiceFactory()));
    mxDesktop.set(frame::Desktop::create(mxComponentContext));
}

but that gives the error
setUp() failed
- An uncaught exception of type com.sun.star.uno.DeploymentException
- component context fails to supply service com.sun.star.frame.Desktop 
of type com.sun.star.frame.XDesktop2

The same error with
void DrawTest::setUp()
{
    BootstrapFixture::setUp();
    m_xContext = comphelper::getProcessComponentContext();
    mxDesktop.set(frame::Desktop::create(m_xContext));
}

And here the assertion fails
void DrawTest::setUp()
{
    BootstrapFixture::setUp();
    m_xImpressComponent =

getMultiServiceFactory()->createInstance("com.sun.star.comp.presentation.PresentationDocument");
    CPPUNIT_ASSERT_MESSAGE("no m_xImpressComponent", 
m_xImpressComponent.is());
}

HowTo load a file in unit test in xmloff?

Kind regards
Regina