def METHOD_NAME(self):
    """
    Test that blocks used from a library can have children.
    """
    library = LibraryFactory.create(modulestore=self.store)
    # In the library, create a vertical block with a child:
    vert_block = BlockFactory.create(
        category="vertical",
        parent_location=library.location,
        user_id=self.user_id,
        publish_item=False,
        modulestore=self.store,
    )
    child_block = BlockFactory.create(
        category="html",
        parent_location=vert_block.location,
        user_id=self.user_id,
        publish_item=False,
        metadata={"data": "Hello world", },
        modulestore=self.store,
    )
    assert child_block.parent.replace(version_guid=None, branch=None) == vert_block.location