Set up reloading after_initialize

Fixes #336

Before this commit, the initialization process 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

The double reloading of factory_bot in this initialization is not ideal,
but also shouldn't generally cause any problems on its own.

The problems people are having in #336 come from the fact that
I18n gets set up in an `after_initialize` callback, but factory_bot gets
reloaded before the `after_initialize` callbacks are triggered.
If the `FactoryBot.define` block references any code that uses I18n
translations as it loads, that code will raise an error (references
inside other factory_bot methods, or code that uses I18n translations
inside of methods still works fine, since the whole Rails initialization
process would be complete by the time any of that code runs).

This commit moves factory_bot reloading from a prepare callback into an
`after_initialize` callback. This allows us to avoid reloading
factory_bot before I18n is loaded, and also gets rid of that pesky
double reloading of factory_bot.

The new initialization process looks like:

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. Run the factory_bot reloader, which sets up the prepare callback for
any future prepares (for example calling `reload!` in the console), and
executes the reloader to run the initial `FactoryBot.reload`

[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 +18,8 @@ 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|
+      Reloader.new(app).run
     end
 
     private

lib/factory_bot_rails/reloader.rb

@@ -4,21 +4,22 @@ 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
 
     def run
       return unless @paths.any?
 
-      register_reloader(build_reloader)
+      reloader = build_reloader
+      register_reloader(reloader)
+      reloader.execute
     end
 
     private
 
-    attr_reader :app, :config
+    attr_reader :app
 
     def build_reloader
       reloader_class.new(@paths.files, @paths.directories) do
@@ -31,11 +32,11 @@ module FactoryBotRails
     end
 
     def register_reloader(reloader)
-      config.to_prepare do
+      app.reloaders << reloader
+
+      app.reloader.to_prepare do
         reloader.execute
       end
-
-      app.reloaders << reloader
     end
   end
 end

spec/factory_bot_rails/reloader_spec.rb

@@ -12,8 +12,6 @@ describe FactoryBotRails::Reloader do
 
     context "when a definition file paths exist" do
       it "registers a reloader" do
-        allow(reloader_class).to receive(:new)
-
         run_reloader(["spec/fixtures/factories", "not_exist_directory"])
 
         expect(reloader_class).to have_received(:new)
@@ -22,8 +20,6 @@ describe FactoryBotRails::Reloader do
 
     context "when a file exists but not a directory" do
       it "registers a reloader" do
-        allow(reloader_class).to receive(:new)
-
         run_reloader(["spec/fake_app", "not_exist_directory"])
 
         expect(reloader_class).to have_received(:new)
@@ -32,8 +28,6 @@ describe FactoryBotRails::Reloader do
 
     context "when a definition file paths NOT exist" do
       it "does NOT register a reloader" do
-        allow(reloader_class).to receive(:new)
-
         run_reloader(["not_exist_directory"])
 
         expect(reloader_class).not_to have_received(:new)
@@ -42,12 +36,24 @@ describe FactoryBotRails::Reloader do
 
     def run_reloader(definition_file_paths)
       FactoryBot.definition_file_paths = definition_file_paths
-      FactoryBotRails::Reloader.
-        new(Rails.application, Rails.application.config).run
+      FactoryBotRails::Reloader.new(app).run
+    end
+
+    def app
+      double(
+        :app,
+        config: double(:config, file_watcher: reloader_class),
+        reloader: double(:reloader, to_prepare: nil),
+        reloaders: [],
+      )
     end
 
     def reloader_class
-      Rails.application.config.file_watcher
+      @reloader_class ||=
+        double(
+          :reloader_class,
+          new: double(:reloader, execute: nil),
+        )
     end
   end
 end