Handle missing sw.js in test environment assets (#39459)

lib/mastodon/middleware/public_file_server.rb

@@ -5,8 +5,9 @@ require 'action_dispatch/middleware/static'
 module Mastodon
   module Middleware
     class PublicFileServer
+      CACHE_TTL = 28.days.to_i
+      SERVICE_WORKER_PATH = '/sw.js'
       SERVICE_WORKER_TTL = 7.days.to_i
-      CACHE_TTL          = 28.days.to_i
 
       def initialize(app)
         @app = app
@@ -24,7 +25,7 @@ module Mastodon
         # Set cache headers on static files. Some paths require different cache headers
         request = Rack::Request.new env
         headers['cache-control'] = begin
-          if request.path.start_with?('/sw.js')
+          if request.path.start_with?(SERVICE_WORKER_PATH)
             "public, max-age=#{SERVICE_WORKER_TTL}, must-revalidate"
           elsif request.path.start_with?(paperclip_root_url)
             "public, max-age=#{CACHE_TTL}, immutable"

spec/requests/public_files_spec.rb

@@ -6,8 +6,10 @@ RSpec.describe 'Public files' do
   include RoutingHelper
 
   context 'when requesting service worker file' do
+    before { stub_const 'Mastodon::Middleware::PublicFileServer::SERVICE_WORKER_PATH', '/robots.txt' }
+
     it 'returns the file with the expected headers' do
-      get '/sw.js'
+      get Mastodon::Middleware::PublicFileServer::SERVICE_WORKER_PATH
 
       expect(response)
         .to have_http_status(200)