So, this is a thing:
bundle install --without development:test
...
...
Bundle complete! XX Gemfile dependencies, XX gems now installed.
Gems in the groups development and test were not installed.
Now,
bundle install
...
...
Bundle complete! XX Gemfile dependencies, XX gems now installed.
Gems in the groups development and test were not installed.
Basically — you run bundle install --without <group> once, and that’s saved in .bundle/config. So next time you run bundle install without any arguments, it won’t install gems in the groups you specify.
It looks like it is fixed in Bundler 2.0, though.