In Rails 4 with rspec_rails, my assert method is from minitest, not from wrong.
Here's an app demonstrating the problem: https://github.com/jjb/rails_4_rspec_rails_wrong
Here's the relevant commit: jjb/rails_4_rspec_rails_wrong@c59d8f4
I tried putting require 'wrong/adapters/minitest' above and below the rspec require in spec_helper, it made no difference.
rspec_rails does all these handy matcher delegations, maybe that contributes to the problem?
I didn't try a pure-rspec experiment. Let me know if you are at a loss and I will try that.