Is intentionally sitting next to women on public transportation to test oneself and remember God considered piety or deception?

What you did was a mistake, and this might be one of Satan's ploys to throw you into trials (fitan). The correct thing is for you to stay away from the vicinity of trials and to ask Allah for well-being and steadfastness. A servant gains strength through his Lord, and no one is freed from the evil of his own self except by Allah's grace, for evil is inherent in the soul. We ask Allah to protect us from the evils of our souls and the wicked consequences of our deeds.