t.Fatalf("write failed: %v", err)
			}
			wroteBytes += n
			wrote.Write(buf[:n])
			debugln("WRITE 4\t", n, wroteBytes)

			// TryWriteByte
			err = rb.TryWriteByte(buf[0])
			if err != nil && err != ErrAcquireLock && err != ErrTooMuchDataToWrite && err != ErrIsFull {
				t.Fatalf("write failed: %v", err)
			}
			if err == nil {
				wroteBytes++

		err = r.setErr(r.writeByte(c), true)
	}
	if r.block && err == nil {
		r.writeCond.Broadcast()
	}
	return err
}

// TryWriteByte writes one byte into buffer without blocking.
// If it has not succeeded to acquire the lock, it return ErrAcquireLock.
func (r *RingBuffer) TryWriteByte(c byte) error {
	ok := r.mu.TryLock()
	if !ok {
		return ErrAcquireLock
	}
	defer r.mu.Unlock()
	if err := r.err; err != nil {