disable webpack proxy in rspec environment due to conflicts with webmock gem

config/initializers/static_files.rb

@@ -16,15 +16,20 @@ if app.config.serve_static_files
   # If webpack-dev-server is configured, proxy webpack's public directory
   # instead of looking for static assets
   if Gitlab.config.webpack.dev_server.enabled
-    app.config.webpack.dev_server.merge!(
+    dev_server = {
       enabled: true,
+      host: Gitlab.config.webpack.dev_server.host,
+      port: Gitlab.config.webpack.dev_server.port,
+      manifest_host: Gitlab.config.webpack.dev_server.host,
+      manifest_port: Gitlab.config.webpack.dev_server.port,
+    }
+
+    if Rails.env.development?
+      dev_server.merge!(
         host: Gitlab.config.gitlab.host,
         port: Gitlab.config.gitlab.port,
         https: Gitlab.config.gitlab.https,
-      manifest_host: Gitlab.config.webpack.dev_server.host,
-      manifest_port: Gitlab.config.webpack.dev_server.port,
       )
-
       app.config.middleware.insert_before(
         Gitlab::Middleware::Static,
         Gitlab::Middleware::WebpackProxy,
@@ -33,4 +38,7 @@ if app.config.serve_static_files
         proxy_port: Gitlab.config.webpack.dev_server.port,
       )
     end
+
+    app.config.webpack.dev_server.merge!(dev_server)
+  end
 end