w.Flush()
		if s := buf.String(); s != "\uFFFD" {
			t.Errorf("WriteRune(%d) wrote %q, not replacement character", r, s)
		}
	}
}

func TestReadStringAllocs(t *testing.T) {
	if asan.Enabled {
		t.Skip("test allocates more with -asan; see #70079")
	}
	r := strings.NewReader("       foo       foo        42        42        42        42        42        42        42        42       4.2       4.2       4.2       4.2\n")