'The opposite of `assertBlockPairIsRelationship`: asserts that a pair
of xblocks do NOT have a certain kind of relationship.'

def assertBlockPairIsNotRelationship(self, xblock1, xblock2, relationships, relationship_type):

    relationship_pairs = self._extract_relationship_pairs(relationships, relationship_type)
    location_pair = self._extract_location_pair(xblock1, xblock2)
    self.assertNotIn(location_pair, relationship_pairs)
