buf.Reset()
		for i := 0; i < n; i++ {
			buf.WriteByte('x')
		}
	}
}

func BenchmarkWriteRune(b *testing.B) {
	const n = 4 << 10
	const r = '☺'
	b.SetBytes(int64(n * utf8.RuneLen(r)))
	buf := NewBuffer(make([]byte, n*utf8.UTFMax))
	for i := 0; i < b.N; i++ {
		buf.Reset()
		for i := 0; i < n; i++ {
			buf.WriteRune(r)
		}
	}
}

// From Issue 5154.

	return func(b *testing.B, n int) {
		buf := bmbuf[0:n]
		o := copy(buf, uchars)
		for o < len(buf) {
			o += copy(buf[o:], uchars)
		}

		// Make space for the needle rune at the end of buf.
		m := utf8.RuneLen(needle)
		for o := m; o > 0; {
			_, sz := utf8.DecodeLastRune(buf)
			copy(buf[len(buf)-sz:], "\x00\x00\x00\x00")
			buf = buf[:len(buf)-sz]
			o -= sz
		}
		buf = utf8.AppendRune(buf[:n-m], needle)