def METHOD_NAME() -> iotests.VM:
    vm = iotests.VM()
    vm.add_blockdev('file,filename=%s,node-name=base-file' % base)
    vm.add_blockdev('%s,file=base-file,node-name=base' % iotests.imgfmt)
    vm.add_blockdev('file,filename=%s,node-name=mid-file' % mid)
    vm.add_blockdev('%s,file=mid-file,node-name=mid,backing=base'
                    % iotests.imgfmt)
    vm.add_drive(top, 'backing=mid,node-name=top')
    return vm