}
		_, err = erasure.Encode(context.Background(), bytes.NewReader(data), writers, buffer, erasure.dataBlocks+1)
		closeBitrotWriters(writers)
		if err != nil {
			t.Fatalf("Test %d: failed to create random test data: %v", i, err)
		}

		readers := make([]io.ReaderAt, len(disks))
		for i, disk := range disks {

func closeBitrotReaders(rs []io.ReaderAt) {
	for _, r := range rs {
		if r != nil {
			if br, ok := r.(io.Closer); ok {
				br.Close()
			}
		}
	}
}

// Close all the writers.
func closeBitrotWriters(ws []io.Writer) {
	for _, w := range ws {
		if w != nil {
			if bw, ok := w.(io.Closer); ok {
				bw.Close()
			}
		}
	}
}

// Returns hash sum for whole-bitrot, nil for streaming-bitrot.