ErrTooMuchDataToWrite = errors.New("too much data to write")

	// ErrIsFull is returned when the buffer is full and not blocking.
	ErrIsFull = errors.New("ringbuffer is full")

	// ErrIsEmpty is returned when the buffer is empty and not blocking.
	ErrIsEmpty = errors.New("ringbuffer is empty")

	// ErrIsNotEmpty is returned when the buffer is not empty and not blocking.
	ErrIsNotEmpty = errors.New("ringbuffer is not empty")

	}

	// read empty
	buf := make([]byte, 1024)
	n, err := rb.Read(buf)
	if err == nil {
		t.Fatalf("expect an error but got nil")
	}
	if err != ErrIsEmpty {
		t.Fatalf("expect ErrIsEmpty but got nil")
	}
	if n != 0 {
		t.Fatalf("expect read 0 bytes but got %d", n)
	}
	if rb.Length() != 0 {
		t.Fatalf("expect len 0 bytes but got %d. r.w=%d, r.r=%d", rb.Length(), rb.w, rb.r)