Refs #37102 - Read real webpack manifest in test

In some test cases (like controller tests) the real manifest isn't
needed, but in integration tests they are.

Rails has deprecated controller tests in favor of integration tests, but
Foreman still has them. This modifies the fake read_webpack_manifest to
read the manifest if available, otherwise pretend it's there.

test/test_helper.rb

@@ -66,9 +66,16 @@ def invalid_name_list
     "\t",
   ]
 end
+
 module ReactjsHelper
   def read_webpack_manifest
-    {"assetsByChunkName" => {"foreman-vendor" => ["foreman-vendor.js", "foreman-vendor.css"]}}
+    manifest = Rails.root.join('public/webpack/manifest.json')
+    if manifest.exist?
+      JSON.parse(manifest.read)
+    else
+      # Stubbed method to deal with a missing manifest for controller tests
+      {"assetsByChunkName" => {"foreman-vendor" => ["foreman-vendor.js", "foreman-vendor.css"]}}
+    end
   end
 end