has_many :through must be defined after the has_many it needs

has_many_through_definition_order_matters.rb

begin
  require "bundler/inline"
rescue LoadError => e
  $stderr.puts "Bundler version 1.10 or later is required. Please update your Bundler"
  raise e
end

gemfile(true) do
  source "https://rubygems.org"
  # Activate the gem you are reporting the issue against.
  gem "activerecord", "5.0.1"
  gem "sqlite3"
end

require "active_record"
require "minitest/autorun"
require "logger"

# Ensure backward compatibility with Minitest 4
Minitest::Test = MiniTest::Unit::TestCase unless defined?(Minitest::Test)

# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table "viewable_products", force: :cascade do |t|
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
  end

  create_table "viewable_products_group_components", force: :cascade do |t|
    t.integer  "viewable_product_id",        null: false
    t.integer  "viewable_products_group_id", null: false
    t.datetime "created_at",                 null: false
    t.datetime "updated_at",                 null: false
    t.index ["viewable_product_id"], name: "index1", using: :btree
    t.index ["viewable_products_group_id"], name: "index2", using: :btree
  end

  create_table "viewable_products_groups", force: :cascade do |t|
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
  end
end

class ViewableProduct < ActiveRecord::Base
  has_many :viewable_products_group_components
  has_many :viewable_products_groups, through: :viewable_products_group_components
end

class ViewableProductsGroup < ActiveRecord::Base
  has_many :viewable_products, through: :viewable_products_group_components
  has_many :viewable_products_group_components # notice the :through is defined first, accidentally
end

class ViewableProductsGroupComponent < ActiveRecord::Base
    belongs_to :viewable_product
    belongs_to :viewable_products_group
end

class BugTest < Minitest::Test
  def test_association_stuff
    group = ViewableProductsGroup.new
    group.viewable_products << ViewableProduct.new
    group.save

    assert_equal true, group.valid?
    assert_equal 1, group.viewable_products.count
  end
end

To fix this failing test, simply move line 54 up one line, so that the has_many :viewable_products_group_components is defined before has_many :viewable_products, through: :viewable_products_group_components