def METHOD_NAME(self, node_name, bitmap_name):
    bitmap = block_dirty_bitmap.get_bitmap_by_name(self.main_vm,
                                                   node_name,
                                                   bitmap_name)
    # check if bitmap exists
    if bitmap is None:
        self.test.fail('Failed to get bitmap')
    # check if bitmap is persistent
    if not bitmap['persistent']:
        self.test.fail('Bitmap should be persistent')