"NameError: wrong constant name" after upgrading Rails 3.2 to 4.2 – Facebook api

I’m upgrading a Rails app from 3.2 to 4.2 and when running tests, I’m getting NameError: wrong constant name (that’s the full error message, nothing saying exactly what it’s trying to constantize). Running a single test using --trace provides no additional info. It does seem like it gets as far as one of my factories (using FactoryGirl, pasted below), but the factory definition looks fine to me.

Test output:

$ bundle exec rake test TEST=test/unit/offer_test.rb --trace
** Invoke test (first_time)
** Execute test
** Invoke test:single (first_time)
** Invoke test:prepare (first_time)
** Execute test:prepare
** Execute test:single
DEPRECATION WARNING: Core extensions are deprecated and will be removed in Squeel 2.0. (called from /path/to/app/config/initializers/squeel.rb:11:in `block in <top (required)>')
DEPRECATION WARNING: [Devise] including `Devise::TestHelpers` is deprecated and will be removed from Devise.
For controller tests, please include `Devise::Test::ControllerHelpers` instead.
 (called from include at /path/to/app/test/test_helper.rb:15)
DEPRECATION WARNING: [Devise] including `Devise::TestHelpers` is deprecated and will be removed from Devise.
For controller tests, please include `Devise::Test::ControllerHelpers` instead.
 (called from include at /path/to/app/test/test_helper.rb:23)
Run options: --seed 32894

# Running:

EEE

Finished in 0.445273s, 6.7374 runs/s, 0.0000 assertions/s.

  1) Error:
OfferTest#test_should_know_if_accepted_or_not:
NameError: wrong constant name 
    test/unit/offer_test.rb:8:in `setup'


  2) Error:
OfferTest#test_should_not_be_able_to_create_offer_on_ended_listing:
NameError: wrong constant name 
    test/unit/offer_test.rb:8:in `setup'


  3) Error:
OfferTest#test_should_create_new_from_hash_and_properly_set_all_attributes:
NameError: wrong constant name 
    test/unit/offer_test.rb:8:in `setup'

3 runs, 0 assertions, 0 failures, 3 errors, 0 skips
Coverage report generated for Unit Tests to /path/to/app/coverage. 1540 / 21634 LOC (7.12%) covered.

Gemfile:

source 'http://rubygems.org'

ruby '2.1.8'

gem 'rails', '4.2.8'
gem 'rake', '0.9.2.2'

# Gems used only for assets and not required in production environments by default.
gem 'sass-rails', "~> 5.0.6"
gem 'coffee-rails', "~> 4.2.1"
gem 'uglifier', ">= 1.0.3"

# Backwards compat gems used when upgrading from Rails 3 to 4.
gem 'protected_attributes', '~> 1.1.3'
gem 'activerecord-deprecated_finders', '~> 1.0.4', require: 'active_record/deprecated_finders'

gem 'json', '~> 1.8.6'
gem 'pg'
gem 'unicorn'
gem 'jquery-rails'
gem 'slim', '~> 3.0.7' # HTML templating
gem 'devise', '~> 4.2.1' # Authentication
gem 'sidekiq', '~> 4.2.10'
gem 'sidekiq-middleware', '~> 0.3.0'
gem 'sidekiq_status', '~> 1.2.0'
gem 'sinatra', :require => false # For Sidekiq monitoring
gem 'dalli' # memcached used for Rails.cache and sessions
gem 'kgio' # Nonblocking I/O for Ruby - performance boost to dalli
gem 'fog', '~> 1.40.0' # Storage on S3 for carrierwave
gem 'fog-aws', '~> 1.3.0'
gem 'carrierwave', '~> 1.0.0'
gem 'mini_magick'
gem 'filepicker-rails', '~> 2.1.0' # Image uploading
gem 'squeel', '~> 1.2.3'
gem 'stripe', '~> 2.4.0' # Payments
gem 'kaminari', '~> 1.0.1'
gem 'setler' # Settings
gem 'utf8-cleaner' # Rack middleware for cleaing up URL params
gem 'rakismet' # Filtering for spam via akismet.com
gem 'sanitize' # Add attributes like nofollow/target to anchors (per initializer config)
gem 'geokit-rails' # old free geocoding
gem 'geocoder' # new free geocoding
gem 'airbrake', '~> 6.0' # Error notifications
gem 'ancestry', '~> 2.2.2'
gem 'easy_money'
gem 'easypost', '~> 2.7.0' # Shipping
gem 'sift', '~> 2.1.0.1' # Fraud prevention
gem 'paypal-sdk-adaptivepayments' # Used for split payments.
gem 'paypal-sdk-adaptiveaccounts', :require => false # Verify PayPal email
gem 'paypal-sdk-rest', :require => false # REST API client
gem 'friendly_id'
gem 'font_assets'
gem 'griddler', '~> 1.4.0' # incoming emails for conversations
gem 'griddler-sendgrid', '~> 1.0.0'
gem 'aws-sdk', '~> 2.9.9'
gem 'text'
gem 'mailhopper'
gem 'audited-activerecord', '~> 4.2.2'
gem 'acts_as_list', '~> 0.9.5' # Used for sorting images
gem 'newrelic_rpm', '~> 4.1.0.333'
gem 'httpclient'
gem 'httparty'
gem 'rest-client', '~> 2.0.1' # for handling POST's to API images
gem 'hipchat'
gem 'musicbrainz' # Used to fetch album art.
gem 'bourbon', '~> 4.3.4' # Sass mixins libraries
gem 'armor_payments' # Escrow
gem 'countries', require: 'countries/global'
gem 'koala' # Facebook API tools
gem 'twilio-ruby' # Twilio text-messaging API
gem 'createsend' # Campaign Monitor integration
gem 'oink' # memory usage logger
gem 'browser', '~> 2.3.0' # used to detect mobile user-agent
gem 'redis-namespace', '~> 1.5.3'

group :development do
  gem 'brakeman', :require => false
  gem 'pry-rails'
  gem 'redcarpet' # for YARD doc markdown formatting
  gem 'yard'
  gem 'rails-footnotes'
end

group :test do
  gem 'database_cleaner'
  gem 'email_spec'
  gem 'minitest', '~> 5.10.1'
  gem 'mocha', :require => false # Mocha needs to be required after the env is set up. See test/test_helper.rb
  gem 'shoulda-matchers'
  gem 'simplecov', :require => false
  gem 'stripe-ruby-mock' # Mocking Stripe requests
  gem 'webmock' # stubbing HTTP requests
end

group :development, :test do
  gem 'byebug' # Debugger for Ruby >= 2.0
  gem 'foreman'
  gem 'forgery' # For randomly generating seed data in dev environment
  gem 'factory_girl_rails', '~> 4.8.0' # Used mostly in tests
  gem 'rspec', '~> 3.5.0'
  gem 'rspec-rails', '~> 3.5.2'
  gem 'faraday' # HTTP stubbing for vcr
  # gem 'mailcatcher' # Capture and display local mailers. NOTE: Recommended to not be in Gemfile: https://github.com/sj26/mailcatcher#bundler
  gem 'net-http-spy', :require => false
  # gem 'rack-mini-profiler' # Displays a speed badge for every html page
  gem 'vcr' # 'Playback' canned HTTP responses when testing

  # Generate Database Diagram; Must install Graphviz to use locally (`brew install graphviz`, etc)
  # gem 'rails-erd'
  # rake db_diagram
end

test/unit/offer_test.rb

require 'test_helper'

class OfferTest < ActiveSupport::TestCase

  def setup
    @buyer = FactoryGirl.create(:user, username: 'test_buyer')
    @seller = FactoryGirl.create(:user, username: 'test_seller')
    @listing = FactoryGirl.create(:listing, auction: false)  # <-- This is line 8, where the test throws the NameError.
    @offer = FactoryGirl.create(:offer, buyer: @buyer, listing: @listing)
  end

  # ...snip...
end

Listings factory:

FactoryGirl.define do
  factory :listing do |l|
    l.association :category
    l.association :seller, factory: :user

    l.age { [3, 3, 9, 9, 10].sample }
    l.album_art_url { media.present? ? "http://example.com/images/#{rand(1000)}.png" : nil }
    l.album_art_back_url { media.present? ? "http://example.com/images/#{rand(1000)}-back.png" : nil }
    l.auction_opening_bid { Forgery(:monetary).formatted_money }
    l.auction_reserve_price { Forgery(:monetary).formatted_money }
    l.bold { (rand(2) == 0) }
    l.box_count 1
    l.brand { Forgery(:name).company_name }
    l.classified_asking_price_dollars { Forgery(:monetary).formatted_money(min: 1) }
    l.condition { rand(10) + 1 }
    l.description { Forgery(:lorem_ipsum).sentences(20) }
    l.hit_count { Forgery(:basic).number(at_most: 69) }
    l.media false
    l.product_name { Forgery(:basic).text }
    l.no_transaction_fee false
    l.payment_methods ["PERS", "DISC"]
    l.retail_price_dollars { Forgery(:monetary).formatted_money }
    l.ship_from "29601"
    l.ship_to "US"
    l.shipping_methods ["UPS", "FDX"]
    l.status Listing::STATUSES[:active]
    l.title { Forgery(:basic).text }
    l.auction_duration 7
  end

  factory :listing_with_shipping_info, parent: :listing do |l|
    after(:create) do |listing|
      address = FactoryGirl.create(:address, user: listing.seller)
      listing.shipment.update_attributes(seller_address: address)
    end
  end
end