In [this PR](https://github.com/localstack/localstack/pull/1200/files) we introduced a new way of starting S3 in a separate process.

In the meantime, the service startup has been significantly reworked, and it seems that we can integrate the S3 starter into the [`multiserver.py`](https://github.com/localstack/localstack/blob/master/localstack/utils/server/multiserver.py) based loading approach that loads multiple APIs in a single process, for performance reasons. We should look into that.
bucket_name = 'test-bucket-%s' % short_uid()
        self.s3_client.create_bucket(Bucket=bucket_name)
        body = 'something body'
        
        object_key = 'test-presigned-post-key'
        presigned_request = self.s3_client.generate_presigned_post(
            Bucket=bucket_name,
            Key=object_key
        )
        
        files = {'file': body}
        response = requests.post(presigned_request['url'], data=presigned_request['fields'], files=files, verify=False)
        self.assertEqual(response.status_code, 200)
        
        downloaded_object = self.s3_client.get_object(Bucket=bucket_name, Key=object_key)
        download_object = downloaded_object['Body'].read()
        self.assertEqual(to_str(body), to_str(download_object))
        
        self._delete_bucket(bucket_name, [object_key])
    def test_s3_delete_response_content_length_zero(self):