Rails tests don't seem to be loading any classes, NameError: uninitialized constant

Suddenly whenever I run 'rake test' or 'bundle exe rake test' I get the following error.

NameError: uninitialized constant FactoryGirl

Before anyone tells me to add require 'factory_girl' to my test_helper.rb file, the same updated branch is running the tests without any problem in another computer.

Still I've tried adding require 'factory_girl'. Then it raised another error saying NameError: uninitialized constant Faker, and so I added require 'faker' and there was always something it required, and the tests for this project always worked fine without all those requires.

Info that might be useful:

• Ubuntu 16.10
• Rails 5.1.1
• Ruby 2.3.3 (using rbenv)
• I'm using minitest, not RSPEC

Error bracktrace:

** Invoke test (first_time)
** Execute test
rake aborted!
NameError: uninitialized constant FactoryGirl
/home/samir/Projects/Tuuris/test/test_helper.rb:10:in `<top (required)>'
/home/samir/Projects/Tuuris/test/controllers/admin_controller_test.rb:1:in `<top (required)>'
/home/samir/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/railties-5.1.1/lib/rails/test_unit/test_requirer.rb:14:in `block in require_files'
/home/samir/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/railties-5.1.1/lib/rails/test_unit/test_requirer.rb:13:in `each'
/home/samir/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/railties-5.1.1/lib/rails/test_unit/test_requirer.rb:13:in `require_files'
/home/samir/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/railties-5.1.1/lib/rails/test_unit/minitest_plugin.rb:67:in `rake_run'
/home/samir/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/railties-5.1.1/lib/rails/test_unit/testing.rake:14:in `block in <top (required)>'
/home/samir/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/rake-12.0.0/lib/rake/task.rb:250:in `block in execute'
/home/samir/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/rake-12.0.0/lib/rake/task.rb:250:in `each'
/home/samir/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/rake-12.0.0/lib/rake/task.rb:250:in `execute'
/home/samir/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/rake-12.0.0/lib/rake/task.rb:194:in `block in invoke_with_call_chain'
/home/samir/.rbenv/versions/2.3.3/lib/ruby/2.3.0/monitor.rb:214:in `mon_synchronize'
/home/samir/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/rake-12.0.0/lib/rake/task.rb:187:in `invoke_with_call_chain'
/home/samir/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/rake-12.0.0/lib/rake/task.rb:180:in `invoke'
/home/samir/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/rake-12.0.0/lib/rake/application.rb:152:in `invoke_task'
/home/samir/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/rake-12.0.0/lib/rake/application.rb:108:in `block (2 levels) in top_level'
/home/samir/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/rake-12.0.0/lib/rake/application.rb:108:in `each'
/home/samir/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/rake-12.0.0/lib/rake/application.rb:108:in `block in top_level'
/home/samir/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/rake-12.0.0/lib/rake/application.rb:117:in `run_with_threads'
/home/samir/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/rake-12.0.0/lib/rake/application.rb:102:in `top_level'
/home/samir/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/rake-12.0.0/lib/rake/application.rb:80:in `block in run'
/home/samir/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/rake-12.0.0/lib/rake/application.rb:178:in `standard_exception_handling'
/home/samir/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/rake-12.0.0/lib/rake/application.rb:77:in `run'
/home/samir/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/rake-12.0.0/exe/rake:27:in `<top (required)>'
/home/samir/.rbenv/versions/2.3.3/bin/rake:22:in `load'
/home/samir/.rbenv/versions/2.3.3/bin/rake:22:in `<main>'
Tasks: TOP => test

Any clue?