Add test to make sure the sprockets cache is not shared per environment

Gemfile.lock

@@ -116,7 +116,7 @@ GEM
       coffee-script-source
       execjs
     coffee-script-source (1.10.0)
-    concurrent-ruby (1.0.0)
+    concurrent-ruby (1.0.1)
     connection_pool (2.2.0)
     dalli (2.7.6)
     dante (0.2.0)
@@ -239,7 +239,7 @@ GEM
     sprockets (3.5.2)
       concurrent-ruby (~> 1.0)
       rack (> 1, < 3)
-    sprockets-rails (3.0.2)
+    sprockets-rails (3.0.4)
       actionpack (>= 4.0)
       activesupport (>= 4.0)
       sprockets (>= 3.0.0)

railties/test/application/assets_test.rb

@@ -186,6 +186,26 @@ module ApplicationTests
       assert_file_exists("#{app_path}/public/assets/something-*.js")
     end
 
+    test 'sprockets cache is not shared between environments' do
+      app_file "app/assets/images/rails.png", "notactuallyapng"
+      app_file "app/assets/stylesheets/application.css.erb", "<%= asset_path('rails.png') %>"
+      add_to_env_config 'production', 'config.assets.prefix = "production_assets"'
+
+      precompile!
+
+      assert_file_exists("#{app_path}/public/assets/application-*.css")
+
+      file = Dir["#{app_path}/public/assets/application-*.css"].first
+      assert_match(/assets\/rails-([0-z]+)\.png/, File.read(file))
+
+      precompile! RAILS_ENV: 'production'
+
+      assert_file_exists("#{app_path}/public/production_assets/application-*.css")
+
+      file = Dir["#{app_path}/public/production_assets/application-*.css"].first
+      assert_match(/production_assets\/rails-([0-z]+)\.png/, File.read(file))
+    end
+
     test 'precompile use assets defined in app config and reassigned in app env config' do
       add_to_config 'config.assets.precompile = [ "something_manifest.js" ]'
       add_to_env_config 'production', 'config.assets.precompile += [ "another_manifest.js" ]'