// create a window at 50, 50 with size 100, 100
QGLMockView glw;
qDebug() << "glw.geometry()" << glw.geometry();
qDebug() << "glw.frameGeometry()" << glw.frameGeometry();
qDebug() << "glw.frameMargins()" << glw.frameMargins();

Result is on Windows:

QDEBUG : tst_QGLAbstractSurface::glWindowSurface() glw.geometry() QRect(50,50 104x100) 
QDEBUG : tst_QGLAbstractSurface::glWindowSurface() glw.frameGeometry() QRect(46,27 112x127) 
QDEBUG : tst_QGLAbstractSurface::glWindowSurface() glw.frameMargins() QMargins(4, 23, 4, 4) 

This defeats the code in viewportGL() in the QGLWindowSurface, and results in failing unit tests.

This QPA behaviour on Windows appears to be buggy. Need to create a minimal example to show that the Windows QPA plugin code is wrong, and ask for a fix; or fix the problem in Qt3D.