Custom RSpec be_square matcher for CarrierWave

It seems to me that when using CarrierWave for image uploads, particularly user avatars, it would be a pretty common thing to generate at least one square-cropped version of the image. CarrierWave ships with some nice custom matchers to test exact dimensions and such, but I found I wanted a way to just test that an image was square.

I did this using by building a custom matcher on top of the ones CarrierWave provides. If you have the conventional spec_helper.rb that requires support/**/*.rb, then you can just drop this somewhere like support/matchers/carrierwave_matchers.rb:

Then, you can use this like: