const BufSize = 1000
	b := NewWriterSize(new(bytes.Buffer), BufSize)
	// Does it recognize itself?
	b1 := NewWriterSize(b, BufSize)
	if b1 != b {
		t.Error("NewWriterSize did not detect underlying Writer")
	}
	// Does it wrap if existing buffer is too small?
	b2 := NewWriterSize(b, 2*BufSize)
	if b2 == b {
		t.Error("NewWriterSize did not enlarge buffer")
	}
}

type Writer struct {
	err error
	buf []byte
	n   int
	wr  io.Writer
}

// NewWriterSize returns a new [Writer] whose buffer has at least the specified
// size. If the argument io.Writer is already a [Writer] with large enough
// size, it returns the underlying [Writer].
func NewWriterSize(w io.Writer, size int) *Writer {
	// Is it already a Writer?
	b, ok := w.(*Writer)
	if ok && len(b.buf) >= size {