'Assert a number of conditions that must be true for `block` to be good.'

def assert_xblocks_are_good(self, block):

    scope_ids = block.scope_ids
    self.assertIsNotNone(scope_ids.usage_id)
    self.assertIsNotNone(scope_ids.def_id)
    for child_id in block.children:
        child = block.runtime.get_block(child_id)
        self.assert_xblocks_are_good(child)
