Rails: AbstractController::Helpers::MissingHelperError - Missing helper file application_helper.rb_helper.rb

This worked for me:

cd ~
mv sites tmpsites
mv tmpsites sites

I also did this, but am unsure if it was required:

cd /
sudo ln -s Users users

Oddly, I can't see the lowercase users symlink, but both ls /users and ls /Users work.

I solved with "spring stop" in the console.

Step-by-Step Guide:

On OSX, I had changed my username to Psy from psy. So figuring the problem out was a pain in the ass. Following these steps helped me out:

Run irb and execute this command in your project folder:

File.expand_path("./")
# => "/Users/psy/code/rails_app"

Now exit irb and run this command in your shell:
```
$ pwd
# => /Users/Psy/code/rails_app
```
Compare the two and notice the directory with the case difference, in this case it's Psy
Rename that directory to anything, and then rename it back to the original folder (use sudo only if necessary)
```
$ sudo mv /Users/Psy /Users/tmp
$ sudo mv /Users/tmp /Users/Psy
```