Setup StimulusReflex testing [add gem]

Surprisingly, the StimulusReflex framework [doesn't have many resources for testing](https://docs.stimulusreflex.com/appendices/testing.html), but thankfully someone's made a gem.

Gemfile

@@ -159,6 +159,7 @@ group :test, :development do
   gem 'rspec-retry', require: false
   gem 'rswag-specs'
   gem 'shoulda-matchers'
+  gem 'stimulus_reflex_testing'
   gem 'timecop'
 end
 

Gemfile.lock

@@ -705,6 +705,8 @@ GEM
       rack (>= 2, < 4)
       railties (>= 5.2, < 8)
       redis (>= 4.0, < 6.0)
+    stimulus_reflex_testing (0.3.0)
+      stimulus_reflex (>= 3.3.0)
     stringex (2.8.6)
     stripe (8.6.0)
     swd (1.3.0)
@@ -899,6 +901,7 @@ DEPENDENCIES
   spring-commands-rspec
   state_machines-activerecord
   stimulus_reflex (= 3.5.0.rc3)
+  stimulus_reflex_testing
   stringex (~> 2.8.5)
   stripe
   timecop

spec/reflex_helper.rb

@@ -0,0 +1,4 @@
+# frozen_string_literal: true
+
+require "base_spec_helper"
+require "stimulus_reflex_testing/rspec"

spec/reflexes/products_reflex_spec.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+require "reflex_helper"
+
+describe ProductsReflex, type: :reflex do
+
+end