The Bechdel test is too incomplete to be effective.
1. It doesn't cover the case when the lead character is female.
Example: A woman has only one minor female friend, all other characters are male. (will pass the test, but female characters are still underrepresented)
Example: Tomb raider-like movies (will fail the test, although Lara Croft is a strong badass female character, just because she spends all her time kicking men's asses)
2. It doesn't cover the case when no character is interacting with characters other than the lead character.
Example: a boy raised in a world where everyone else is a woman. None of the people the boy interacts with know each other. (will fail the test, but female characters are overrepresented)
3. It doesn't cover stories with less than 4 characters.
Example: a man and a woman lost on a island