The Bechdel test is a famous test of film to measure whether a movie represents women as more than just accessories for the male cast. Specifically, the test is passed if a film features two women who have a conversation about something other than a man. Surprisingly, a lot of films fail this test.

It isn't surprising for a few reasons.

1. A lot of movies, which the test highlights, have female characters that are not really fleshed out because of sexism. They only exist for the real characters, the men!
2. A lot of movies don't have female characters because of the setting, like The Shawshank Redemption. An all men's prison just isn't going to have women in it. Small cast movies in similar all male settings are also not surprising to fail the test.
3. Some movies are all about a main character and there aren't scenes that don't discuss the main character. So a conversation that doesn't include the main character would be forced in just to meet the test.

Now, while it isn't surprising that a lot of movies fail the test, the real purpose of the test is to show how all three types of movies are massively over represented in the number of movies made. #3 is an issue overall because of how the vast majority of main characters are men and not women. #2 is an issue overall because of how many movies there are about all male settings. It highlights the overall trend that main characters are men and the movies are all about the men, and wouldn't be an issue if there were just as many movies about women or with casts that only include women. The Descent stands out with all characters being women because that is very rare!

So if a single movie fails the test because of the setting or small cast, it isn't necessarily a bad thing. If there is a diverse cast, but the women are not fleshed out then it is an issue. If a movie could have included women, but they were too lazy to do so and to give them characterization, then it is an issue.