func findFileName() (*string, error) {
	pc := make([]uintptr, 100)
	count := runtime.Callers(0, pc)
	frames := runtime.CallersFrames(pc[:count])
	var lastFrame *runtime.Frame
	var testFrame *runtime.Frame

	for {
		frame, more := frames.Next()
		if !more {
			break
		}

		if isTestRunnerFrame(&frame) {
			testFrame = &frame
			break
		}
		lastFrame = &frame
	}

	if !isTestRunnerFrame(testFrame) {
		return nil, fmt.Errorf("approvals: could not find the test method")
	}

	return &lastFrame.File, nil
}

func isTestRunnerFrame(f *runtime.Frame) bool {
	return f != nil && f.Function == "testing.tRunner" || f.Function == "testing.runExample"
}