Use CPPUNIT_ASSERT instead of assert.

Change-Id: I24e7934002ebdde208db74ae3308b26875a3155b
diff --git a/libreofficekit/qa/unit/tiledrendering.cxx b/libreofficekit/qa/unit/tiledrendering.cxx
index b231eb0..9c035b4 100644
--- a/libreofficekit/qa/unit/tiledrendering.cxx
+++ b/libreofficekit/qa/unit/tiledrendering.cxx
@@ -77,7 +77,7 @@ void TiledRenderingTest::testOverlay()

    scoped_ptr< Office > pOffice( lok_cpp_init(
                                      sLOPath.c_str() ) );
    assert( pOffice.get() );
    CPPUNIT_ASSERT( pOffice.get() );

    scoped_ptr< Document> pDocument( pOffice->documentLoad(
                                         sDocPath.c_str() ) );