aws-support/src/main/java/com/streamsets/pipeline/lib/aws/s3/S3Accessor.java
TransferManager createTransferManager(AmazonS3 s3Client) throws StageException {
    return createTransferManagerBuilder().withS3Client(s3Client)
                                         .withExecutorFactory(
                                             createExecutorFactory(transferManagerConfigs.getThreads())
                                         )
                                         .withShutDownThreadPools(true)
                                         .withMinimumUploadPartSize(transferManagerConfigs.getMinimumUploadPartSize())
                                         .withMultipartUploadThreshold(transferManagerConfigs
                                             .getMultipartUploadThreshold())
                                         .build();
  }
TransferManager createTransferManager(AmazonS3 s3Client) throws StageException {
    return createTransferManagerBuilder().withS3Client(s3Client)
                                         .withExecutorFactory(
                                             createExecutorFactory(transferManagerConfigs.getThreads())
                                         )
                                         .withShutDownThreadPools(true)
                                         .withMinimumUploadPartSize(transferManagerConfigs.getMinimumUploadPartSize())
                                         .withMultipartUploadThreshold(transferManagerConfigs
                                             .getMultipartUploadThreshold())
                                         .build();
  }
visible for testing