// that could mean it just didn't run long enough, try with a
	// longer duration.
	for {
		var prof bytes.Buffer
		if err := StartCPUProfile(&prof); err != nil {
			t.Fatal(err)
		}
		f(duration)
		StopCPUProfile()

		if p, ok := profileOk(t, matches, prof, duration); ok {
			return p
		}

		duration *= 2
		if time.Until(deadline) < duration {
			break
		}

func (f matchStringOnly) MatchString(pat, str string) (bool, error)   { return f(pat, str) }
func (f matchStringOnly) StartCPUProfile(w io.Writer) error           { return errMain }
func (f matchStringOnly) StopCPUProfile()                             {}
func (f matchStringOnly) WriteProfileTo(string, io.Writer, int) error { return errMain }
func (f matchStringOnly) ImportPath() string                          { return "" }