Are their any medical tests or devices in usa that can tell the number of boys a girl has done sex with?

Yes: There is one "test". You just ask the person (but be sure you have a reason to ask). A girl can ask a guy how many people he has had sex with. Likewise, a guy can ask a girl how many people she has had sex with. This "test" has better accuracy when guys are being asked, because there is more negative stigma for a girl to have had several sex partners. To be fair, stigma should also apply to guys.

No: There is no "medical test" that gives the "mileage" on a woman's bottom.The presence or absence of a hymen that bleeds with sex is not a reliable indicator of virginity.Your questions are valid ones. But the emotion behind it is troubling. Sex should be a shared experience when you are ready.It should not be given or taken. Sort out the reasons before answering related questions.