Passing the 'friend test' can be difficult and intimidating. The first time you meet his friends, it can feel like all of them are looking at you and all of them are judging you. I'm afraid we have bad news for you - they are. But maybe not in the way you suspect of them.
As much as men can seem like overgrown children when they hang out together, they're actually a protective pack and they look out for each other just as much as women do. They want to know you're right for him, and you're not going to have a negative impact on his life. They were also around before you were, and they've known him longer. Men hate it when a woman comes between him and his friends, and sometimes the woman loses that fight if she turns it into one.