Method getElapsedNanoseconds

tests/catch.hpp:12074–12076

       m_nanoseconds = getCurrentNanosecondsSinceEpoch();
    }
    auto Timer::getElapsedNanoseconds() const -> uint64_t {
        return getCurrentNanosecondsSinceEpoch() - m_nanoseconds;
    }
    auto Timer::getElapsedMicroseconds() const -> uint64_t {
        return getElapsedNanoseconds()/1000;
    }