NameError: uninitialized constant Rapidfire Engine Mounted on Root Application Routing did not have a valid gemspec

Question

I have a engine called Questions Engine that has rapidfire as a dependency. Rapidfire is also an engine.

In the question_engine.gemspec I have the gem as both as development and as general dependency

s.add_dependency "rapidfire", "~> 2.0.0"
s.add_development_dependency "rapidfire", "~> 2.0.0"

in my root app gemfile I am loading the question engine inside, my root app has rapidfire on its gemlist

group :development, :test do 

  gem 'question_engine', path: "vendor/engines/QuestionEngine"

end

rapidfire comes with the instructions below

$ bundle install
$ bundle exec rake rapidfire:install:migrations
$ bundle exec rake db:migrate
And if you want to customize rapidfire views, you can do

$ bundle exec rails generate rapidfire:views
Usage

Add this line to your routes will and you will be good to go!

mount Rapidfire::Engine => "/rapidfire"

in my root app config/routes file I have these

Rails.application.routes.draw do
  devise_for :admin_users, ActiveAdmin::Devise.config
  ActiveAdmin.routes(self)
  root 'home#index'
  devise_for :users

  mount FormulaEngine::Engine => "/formula_engine" 
  mount QuestionEngine::Engine, at: 'question_engine' 
  mount Rapidfire::Engine, at: "/rapidfire"
end

when I do rake routes I am getting this error

NameError: uninitialized constant Rapidfire

It worked two days ago. I have checked my commits and I have only worked on server stuff ever since.

The rapidfire generator runs fine inside root app. I already had the tables migrated. Yes the migration files are not getting copied over to the root app but I don't see how the root app doesn't see rapidfire existing?

I am using rails 4.2. The gem supports rails 4 versions according to their docs.

did bundle install, getting this message

question_engine at $HOME/vendor/engines/QuestionEngine did not have a valid gemspec. This prevents bundler from installing bins or native extensions, but that may not affect its functionality. The validation message from Rubygems was: "FIXME" or "TODO" is not a description

here is my gemspec

$:.push File.expand_path("../lib", __FILE__)

# Maintain your gem's version:
require "question_engine/version"

# Describe your gem and declare its dependencies:
Gem::Specification.new do |s|
  s.name        = "question_engine"
  s.version     = QuestionEngine::VERSION
  s.authors     = ["somebody"]
  s.email       = ["somebody@gmail.com"]
  s.homepage    = "TODO"
  s.summary     = "TODO: Summary of QuestionEngine."
  s.description = "TODO: Description of QuestionEngine."
  s.license     = "MIT"

  s.files = Dir["{app,config,db,lib}/**/*", "MIT-LICENSE", "Rakefile", "README.rdoc"]
  s.test_files = Dir["test/**/*"]

  s.add_dependency "rails", "~> 4.2.0"
  s.add_dependency "rapidfire", "~> 2.0.0"

  #s.add_development_dependency "rapidfire", "~> 2.0.0"
  s.add_development_dependency "sqlite3"
end