Back in my dating days I always scheduled a trip early in the relationship. It doesn't have to be long, an extended weekend away will do it. Shared responsibilities, stress, boredom, intimacy, bad weather, finances, etc. If you can add a few dirty diapers you've got a crucible of a marriage in 4-5 days.

Ironically, I threw all my wisdom out the damn window when I met my first wife. And fuck me if I didn't pay for it for decades to come. But that is another story...

[edit] I mentioned this post to my wife not thinking much about it. She pointed out, “Ah, is that why you took me to Paris with you so soon after we met.” To be honest, I can’t remember thinking about asking her as a test. Obviously she passed, as we are together a long time.

From my wife’s side, she told me years after we were together that I had passed a relationship test of hers. As our first “date” (unplanned and a longer story) finished with a kiss and her going to her home and me to mine, I invited her to my place the next night, as I said I was having some people over for a party. She came and we all had a great time. What she told me years later was that she was prepared to show up to my flat and “just by chance” noone else would be there. If I had tried that trick to get her alone at my place she would have left and never returned my calls again.