Set up reloading after_initialize

Alternate fix for #336. We went with #347 instead because the solution
in this commit didn't work with Rails 4.2. Since we are no longer
supporting Rails 4.2, I think this is a better approach.

The original problem looked like this:

Rails runs all of the initializers
1. Run the ["factory_bot.set_factory_paths"][set_factory_paths]
initializer
2. Run the ["factory_bot.register_reloader"][register_reloader]
initializer, which sets up a [prepare callback][]
3. Run the [`:run_prepare_callbacks`][] initializer
4. This triggers the factory_bot [prepare callback][], which causes
factory\_bot to [reload][]

Rails runs `after_initialize` callbacks
1. [I18n initializes]
2. factory\_bot [reloads again][] as described in #334

Triggering the first factory_bot reload before initializing I18n could
cause an error in some cases.

We avoided the problem in #347 by adding a conditional to skip reloading
factory_bot before the application has initialized.

This commit, on the other hand, moves factory_bot reloading from a
prepare callback into an `after_initialize` callback. The initialization
process is now simplified to:

Rails runs all of the initializers
1. Run the ["factory_bot.set_factory_paths"][set_factory_paths]
2. Run the [`:run_prepare_callbacks`][] initializer, which no longer
involves factory_bot

Rails runs `after_intialize` callbacks
1. [I18n initializes]
2. factory_bot loads definitions for the first time. It then runs the
reloader to set up the prepare callback to reload factory_bot when the
application reloads (for example by calling `reload!` in the console),
and to register the reloader to trigger reloads when any factory_bot
definition files change.

[set_factory_paths]: 3815aae2b9/lib/factory_bot_rails/railtie.rb (L17-L19)
[register_reloader]: 3815aae2b9/lib/factory_bot_rails/railtie.rb (L21-L23)
[prepare callback]: https://github.com/thoughtbot/factory_bot_rails/blob/master/lib/factory_bot_rails/reloader.rb#L34-L36
[`:run_prepare_callbacks`]: https://github.com/rails/rails/blob/5-2-stable/railties/lib/rails/application/finisher.rb#L62-L64
[reload]: https://github.com/thoughtbot/factory_bot_rails/blob/master/lib/factory_bot_rails/reloader.rb#L24-L26
[I18n initializes]: 13e2102517/activesupport/lib/active_support/i18n_railtie.rb (L16-L20)
[reloads again]: https://github.com/thoughtbot/factory_bot_rails/blob/master/lib/factory_bot_rails/railtie.rb#L25-L27

lib/factory_bot_rails/railtie.rb

@@ -18,12 +18,9 @@ module FactoryBotRails
       FactoryBot.definition_file_paths = definition_file_paths
     end
 
-    initializer "factory_bot.register_reloader" do |app|
-      Reloader.new(app, config).run
-    end
-
-    config.after_initialize do
-      FactoryBot.reload
+    config.after_initialize do |app|
+      FactoryBot.find_definitions
+      Reloader.new(app).run
     end
 
     private

lib/factory_bot_rails/reloader.rb

@@ -4,9 +4,8 @@ require "factory_bot_rails/definition_file_paths"
 
 module FactoryBotRails
   class Reloader
-    def initialize(app, config)
+    def initialize(app)
       @app = app
-      @config = config
       @paths = DefinitionFilePaths.new(FactoryBot.definition_file_paths)
     end
 
@@ -18,7 +17,7 @@ module FactoryBotRails
 
     private
 
-    attr_reader :app, :config
+    attr_reader :app
 
     def build_reloader
       reloader_class.new(@paths.files, @paths.directories) do
@@ -31,12 +30,8 @@ module FactoryBotRails
     end
 
     def register_reloader(reloader)
-      closed_over_app = app
-
-      config.to_prepare do
-        if closed_over_app.initialized?
-          reloader.execute
-        end
+      app.reloader.to_prepare do
+        reloader.execute
       end
 
       app.reloaders << reloader

spec/factory_bot_rails/reloader_spec.rb

@@ -12,42 +12,74 @@ describe FactoryBotRails::Reloader do
 
     context "when a definition file paths exist" do
       it "registers a reloader" do
-        allow(reloader_class).to receive(:new)
+        file_watcher = file_watcher_double
 
-        run_reloader(["spec/fixtures/factories", "not_exist_directory"])
+        run_reloader(
+          ["spec/fixtures/factories", "not_exist_directory"],
+          file_watcher
+        )
 
-        expect(reloader_class).to have_received(:new)
+        expect(file_watcher).to have_received(:new)
       end
     end
 
     context "when a file exists but not a directory" do
       it "registers a reloader" do
-        allow(reloader_class).to receive(:new)
+        file_watcher = file_watcher_double
 
-        run_reloader(["spec/fake_app", "not_exist_directory"])
+        run_reloader(
+          ["spec/fake_app", "not_exist_directory"],
+          file_watcher
+        )
 
-        expect(reloader_class).to have_received(:new)
+        expect(file_watcher).to have_received(:new)
       end
     end
 
     context "when a definition file paths NOT exist" do
       it "does NOT register a reloader" do
-        allow(reloader_class).to receive(:new)
+        file_watcher = file_watcher_double
 
-        run_reloader(["not_exist_directory"])
+        run_reloader(["not_exist_directory"], file_watcher)
 
-        expect(reloader_class).not_to have_received(:new)
+        expect(file_watcher).not_to have_received(:new)
       end
     end
 
-    def run_reloader(definition_file_paths)
+    def run_reloader(definition_file_paths, file_watcher)
       FactoryBot.definition_file_paths = definition_file_paths
-      FactoryBotRails::Reloader
-        .new(Rails.application, Rails.application.config).run
+      app = app_double(file_watcher)
+      FactoryBotRails::Reloader.new(app).run
     end
 
-    def reloader_class
-      Rails.application.config.file_watcher
+    def file_watcher_double
+      class_double(
+        Rails.application.config.file_watcher,
+        new: double(:reloader, execute: nil)
+      )
+    end
+
+    def app_double(file_watcher)
+      instance_double(
+        Rails.application.class,
+        config: app_config_double(file_watcher),
+        reloader: reloader_double,
+        reloaders: []
+      )
+    end
+
+    def app_config_double(file_watcher)
+      instance_double(
+        Rails.application.config.class,
+        file_watcher: file_watcher
+      )
+    end
+
+    def reloader_double
+      class_double(
+        Rails.application.reloader,
+        to_prepare: nil
+      )
     end
   end
 end