It's a terrible metric. The test would pass if a female developer wrote a simple function and other female developer called it somewhere else. The function need not even do anything at all or be in anyway important to the project. The simple function and the call to it may be the only code contributed to the project by those individuals.
Do we get to feel good about our project and pat ourselves on the back for being progressive after passing this test even though it's utterly meaningless?
Any industry which does not appeal to ~half of its prospective workers might want to spend a bit of time trying to figure out why, instead of getting all defensive and blaming everyone and everything else for the issue.
Why? The logging industry isn't likely losing any sleep over the lack of female lumberjacks and I doubt the child daycare industry cares one iota about the lack of male workers. No one seems to be jumping on their backs about any kind of sex-based disparity and trying to shove inane tests like the above down everyone's throat is going to do more harm than good because it just serves to alienate people.
Men and women are inherently different in some aspects and have different interests. That practically guarantees that there are certain jobs, activities, etc. that are going to appeal to one group more than the other. Unless we have a case of blatant (i.e. no women allowed) discrimination, there's no reason to expect that everything will have a perfect 50-50 balance.