There are so many threads on this.
Floodlights are often turned on in Tests when skies darken; one reason why this may be perceived as unheard of is that few Test grounds actually have them. More importantly, they are no substitute for daylight and play will often become mitigated regardless.
Cricket can be played under lights, but the conditions used in limited overs cricket are quite different; in general, sports played under floodlights use a brightly coloured ball and it's often a very large one. In ODIs, the white ball is changed after 35 overs, a stark contrast from the 80 over change in Tests and while things such as evening dew have also proved a concern, it is the ball that remains the greatest impasse for day/night Tests.
As for the rules of the game, the fact is that Tests are a game of 20 wickets. The bulk of the patience and pressures of Tests are created by the players themselves and if a team opts not to use their wickets, it is still their own decision. If you are to introduce rules that makes that dynamic irrelevant, you might as well just play more ODIs.