Move 'rails initializers' command to Rails::Command

railties/lib/rails/commands/initializers/initializers_command.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+module Rails
+  module Command
+    class InitializersCommand < Base # :nodoc:
+      desc "Print out all defined initializers in the order they are invoked by Rails."
+      def perform
+        require_application_and_environment!
+
+        Rails.application.initializers.tsort_each do |initializer|
+          puts "#{initializer.context_class}.#{initializer.name}"
+        end
+      end
+    end
+  end
+end

railties/test/commands/initializers_test.rb

@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+require "isolation/abstract_unit"
+require "rails/command"
+
+class Rails::Command::InitializersTest < ActiveSupport::TestCase
+  setup :build_app
+  teardown :teardown_app
+
+  test "`rails initializers` prints out defined initializers invoked by Rails" do
+    initial_output = run_initializers_command
+    initial_output_length = initial_output.split("\n").length
+
+    assert_operator initial_output_length, :>, 0
+    assert_not initial_output.include?("set_added_test_module")
+
+    add_to_config <<-RUBY
+      initializer(:set_added_test_module) { }
+    RUBY
+
+    final_output = run_initializers_command
+    final_output_length = final_output.split("\n").length
+
+    assert_equal 1, (final_output_length - initial_output_length)
+    assert final_output.include?("set_added_test_module")
+  end
+
+  private
+    def run_initializers_command
+      rails "initializers"
+    end
+end