Minority woman here.
1.) If it's really a huge concern to you, the best thing to do is probably go to a women's coding group in your local area (try looking on Meetup.com) and talking to the women there. You can ask them pretty candidly how it is at their companies. Only downside is you might miss out on a totally fine company that doesn't have any females yet.
To those saying check if there's a woman on the team already as a metric---eh, if there is that's nice but if there isn't that's not necessarily bad. There are far more men in our field than women. I wouldn't write a company off for just that provided it's a smallish team. I was the first woman and minority on our team. It's fine.
2.) Google the company and maybe also your close team mates. Glassdoor is a good place to check. A bad review or two isn't the end of the world, but if you see a lot stay away. Again downside, a lot of smaller companies don't have many reviews.
3.) You're gonna know if they're lowballing your salary right off the bat when you discuss it during interviews. Make sure you get offers from multiple companies.
4.) You generally can tell a lot from the interview and sometimes you'll have lunch with the team too. Seriously if it's that bad they'll probably show their true colors pretty early on with snide remarks, talking down to you, flirting, etc. I know on a day-to-day basis we women have to brush this off a lot because the world has a lot of creeps. This is not the time to brush it off. Go somewhere else.
5.) No matter how much you try to research ahead of time, sometimes the work environment is just bad. Just as most jobs will have you under a probationary period, you need to do the same to them. Be prepared to leave if it just isn't right. I've seen some people (men and women) just get really wrapped up in the "ideal" of a certain job. Don't fall into that trap.