I know a solid test. Even though I never had trust issues with women in my life as my moto is ‘love is freedom’. They are free to choose any one as long as they don’t do two timing.Same is applicable to me also.
Test : Why girls betray and even if they betray you why they keep you also as a back up option ? Reason is simple. You fulfill their needs. If you suspect your girl is cheating you (Like unavailable to you but always available online to others etc.), stop giving her all material benefits and start asking a few favors. If she pisses off in one or two requests, time to go.