want = append(strconv.AppendInt(want, n, 10), ' ')
		b = append(strconv.AppendInt(b, n, 10), ' ')
		w.Write(b)
	}
	w.Flush()

	if !bytes.Equal(got.Bytes(), want) {
		t.Errorf("output mismatch:\ngot  %s\nwant %s", got.Bytes(), want)
	}
}

// Check that write errors are returned properly.

type errorWriterTest struct {
	n, m   int
	err    error
	expect error
}