The Bechdel test is simple. Your book, film, or other work passes if it contains two named female characters, who speak to each, about something other than a man (or men).
I actually think about this while reading or watching a movie. Some movies that have been hailed as feminist masterpieces (by morons *cough*) don’t pass this test. And some movies I love but which are seen as just awful to women- DO pass.
The corollary I’d give, is that if your work doesn’t pass the Bechdick test as well, you are off the hook. This second test is simple- if your film, book, or other work contains two men, with names, who speak to each other about something other than women, it has passed the test.
Some works contain only one character, two male characters, or a mixed pair. These works are officially off the hook, not liable to the test. Since they wouldn’t pass the Bechdick test, you can’t apply Bechdel to them either.
However, a book that passes one MUST pass the other as well, or it’s simply not realistic. Even fantasy works should maintain enough realism in the characters to make me believe they are real, to flesh them out. If a work doesn’t pass the Bechdel test, I find my suspension of disbelief waning, and my interest in the (male) characters almost lost- since some characters are not realistic, none can be.