如何测试代码执行耗时？

#include <chrono>
#include <ctime>
class Timer
{
public:
    Timer() :running_(false),
        has_run_at_least_once_(false)
    {

    }
    virtual ~Timer()
    {

    }
    virtual void Start()
    {
        if (!running())
        {
            start_cpu_ = std::chrono::high_resolution_clock::now();
            running_ = true;
            has_run_at_least_once_ = true;
        }
    }
    virtual void Stop()
    {
        if (running())
        {
            stop_cpu_ = std::chrono::high_resolution_clock::now();
            running_ = false;
        }
    }
    virtual float Nanoseconds()
    {
        if (!has_run_at_least_once())
        {
            printf("Timer has never been run before reading time.");
            return 0;
        }
        return std::chrono::duration_cast<std::chrono::nanoseconds>(stop_cpu_ - start_cpu_).count();
    }
    virtual float MilliSeconds()
    {
        if (!has_run_at_least_once())
        {
            printf("Timer has never been run before reading time.");
            return 0;
        }
        return std::chrono::duration_cast<std::chrono::milliseconds>(stop_cpu_ - start_cpu_).count();
    }
    virtual float MicroSeconds()
    {
        if (!has_run_at_least_once())
        {
            printf("Timer has never been run before reading time.");
            return 0;
        }
        return std::chrono::duration_cast<std::chrono::microseconds>(stop_cpu_ - start_cpu_).count();
    }
    virtual float Seconds()
    {
        return MilliSeconds() / 1000.0;
    }
    inline bool running() { return running_; }
    inline bool has_run_at_least_once() { return has_run_at_least_once_; }
private:
    bool running_;
    bool has_run_at_least_once_;
    std::chrono::high_resolution_clock::time_point start_cpu_;
    std::chrono::high_resolution_clock::time_point stop_cpu_;
};