My girlfriend bought a pregnancy test for fun?

Only she can answer that. Only she knows if its for fun or if she believes she needs it.

Unless a woman is trying to get pregnant, she doesn't usually want or need a pregnancy test in the house since it is simple to go grab one if accidents or scares happen.

Its a bit unusual actually. Not sure why she would want a pregnancy test for fun. If she was scared that she was pregnant before, but couldn't afford a pregnancy test, then why is she not making sure pregnancy will not happen --> regular birth control, spermicide etc.

You use condoms but do you pull out also? Condoms will only break or slip if they are not put on properly. But condoms can fail. They do not claim to prevent pregnancy 100%, nothing does, so it is always best to use 2 options eg. birth control and condoms or condoms and spermicide. Or 3 options like birth control, condoms and pull out. Condoms, spermicide and pull out. Just making sure that the spermicide is the right one with the condoms you use.

If she couldn't afford a pregnancy test last time, then why waste money for fun now?

It is a bit suspicious. But then she could be stressing and worrying for no reason. Her period could be late or missed for numerous other reasons apart from pregnancy.

Relationships are based on trust, if you do not trust her and question some things that she is saying, then you really need to take time to think about this. If she is not pregnant, does not go on birth control, then for your peace of mind, use condoms, spermicide & pull out. If you do not want to be a father, do the best you can to prevent pregnancy.

If she throws it out, take it out of the trash (I know it's icky) and check it.