Introduce suspenders:tasks generator

Relates to #1159

For now, this generator simply creates `dev.rake` which contains
[dev:prime][].

If future application specific tasks need to be added, we can use this
generator. However, this should not be confused with the existing
pattern of creating tasks under the suspenders namespace, such as the
existing `lib/tasks/suspenders.rake`. Tasks under this namespace cannot
be edited by the consumer, whereas tasks generated by `suspenders:tasks`
are intended to be edited by the consumer.

[dev:prime]: https://thoughtbot.com/blog/priming-the-pump

lib/generators/suspenders/tasks_generator.rb

@@ -0,0 +1,16 @@
+module Suspenders
+  module Generators
+    class TasksGenerator < Rails::Generators::Base
+      source_root File.expand_path("../../templates/tasks", __FILE__)
+      desc <<~TEXT
+        Creates local Rake tasks for development
+
+        bin/rails dev:prime # Sample data for local development environment
+      TEXT
+
+      def create_dev_rake
+        copy_file "dev.rake", "lib/tasks/dev.rake"
+      end
+    end
+  end
+end

lib/generators/templates/tasks/dev.rake

@@ -0,0 +1,12 @@
+if Rails.env.development? || Rails.env.test?
+  require "factory_bot"
+
+  namespace :dev do
+    desc "Sample data for local development environment"
+    task prime: "db:setup" do
+      include FactoryBot::Syntax::Methods
+
+      # create(:user, email: "[email protected]", password: "password")
+    end
+  end
+end

test/generators/suspenders/rake_generator_test.rb

@@ -15,7 +15,7 @@ class RakeGeneratorTest < Rails::Generators::TestCase
         run_generator
 
         assert_file app_root("Rakefile") do |file|
-          assert_match /task default: "suspenders:rake"/, file
+          assert_match(/task default: "suspenders:rake"/, file)
         end
       end
 

test/generators/suspenders/tasks_generator_test.rb

@@ -0,0 +1,38 @@
+require "test_helper"
+require "generators/suspenders/tasks_generator"
+
+module Suspenders
+  module Generators
+    class TasksGeneratorTest < Rails::Generators::TestCase
+      include Suspenders::TestHelpers
+
+      tests Suspenders::Generators::TasksGenerator
+      destination Rails.root
+      teardown :restore_destination
+
+      test "creates dev:prime task" do
+        expected = dev_rake
+
+        run_generator
+
+        assert_file app_root("lib/tasks/dev.rake") do |file|
+          assert_equal expected, file
+        end
+      end
+
+      test "has a custom description" do
+        assert_no_match(/Description:/, generator_class.desc)
+      end
+
+      private
+
+      def dev_rake
+        File.read("./lib/generators/templates/tasks/dev.rake")
+      end
+
+      def restore_destination
+        remove_file_if_exists "lib/tasks/dev.rake"
+      end
+    end
+  end
+end