This commit restores the test deleted in

    https://github.com/rails/rails/commit/fc7c02946783e9417e48c32c9cc28e0181ba623f

Active Record should not test things about autoloading, this would
belong to the railties test suite probably. However, there, it feels
a bit too distant from here.

Imperfect, but on a second thought I believe this trade-off is better.