// and always returns nil.
func (r *RingBuffer) CloseWithError(err error) {
	if err == nil {
		err = io.EOF
	}
	r.setErr(err, false)
}

// CloseWriter closes the writer.
// Reads will return any remaining bytes and io.EOF.
func (r *RingBuffer) CloseWriter() {
	r.setErr(io.EOF, false)
}

// Flush waits for the buffer to be empty and fully read.

			}
			if doSleep && writeRng.Intn(10) == 0 {
				time.Sleep(time.Duration(writeRng.Intn(maxSleep)))
			}
		}
		if err := rb.Flush(); err != nil {
			t.Fatalf("flush failed: %v", err)
		}
		rb.CloseWriter()
	}
	wg.Wait()
	if !errors.Is(readErr, io.EOF) {
		t.Fatalf("expect io.EOF but got %v", readErr)
	}
	if readBytes != wroteBytes {
		a, b := readBuf.Bytes(), wroteBuf.Bytes()