def _send_mail(self, sender, subject, body, html=None):
    self.emails.append((sender, subject, body, html))
Generates a change list for a single collection property change.
dataset/ETHPy150Open GoogleCloudPlatform/appengine-mapreduce/python/test/mapreduce/large_mapreduce_test.py/LargeMapreduceTest._send_mail--crossover with--dataset/ETHPy150Open oppia/oppia/core/domain/collection_services_test.py/_get_collection_change_list