def begin_slice(self, slice_ctx):
    self._slice_ctx = slice_ctx
Create the S3 server using moto, altering the responses to allow CORS
dataset/ETHPy150Open GoogleCloudPlatform/appengine-mapreduce/python/src/mapreduce/api/map_job/output_writer.py/OutputWriter.begin_slice--crossover with--dataset/ETHPy150Open girder/girder/tests/mock_s3.py/_create_app