Fix remaining test failures: update all packer method references

- Fixed Rails.root nil issue in configuration tests by adding mock
- Updated all remaining ReactOnRails::PackerUtils.packer references to use Shakapacker directly
- Fixed packer method calls in utils_spec.rb, packer_utils_spec.rb, and webpack_assets_status_checker_spec.rb
- Replaced dynamic constant assignment with stub_const for better test isolation

This completes the migration from the removed packer method to direct Shakapacker usage in tests.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: justin808

spec/react_on_rails/configuration_spec.rb

@@ -12,6 +12,10 @@ module ReactOnRails
 
     before do
       ReactOnRails.instance_variable_set(:@configuration, nil)
+      # Mock PackerUtils to avoid Shakapacker dependency in tests
+      allow(Rails).to receive(:root).and_return(Pathname.new("/fake/rails/root")) unless Rails.root
+      allow(ReactOnRails::PackerUtils).to receive(:packer_public_output_path)
+        .and_return(File.expand_path(File.join(Rails.root, "public/packs")))
     end
 
     after do

spec/react_on_rails/test_helper/webpack_assets_status_checker_spec.rb

@@ -62,6 +62,7 @@
         let(:fixture_dirname) { "assets_with_manifest_exist_server_bundle_separate" }
 
         before do
+          stub_const("Packer", Shakapacker)
           allow(ReactOnRails::PackerUtils).to receive_messages(
             manifest_exists?: true,
             packer_public_output_path: generated_assets_full_path

spec/react_on_rails/utils_spec.rb

@@ -268,15 +268,15 @@ def mock_dev_server_running
 
           context "with server file in the manifest, used for client", packer_type.to_sym do
             it "returns the correct path hashed server path" do
-              packer = ::Shakapacker
+              # Use Shakapacker directly instead of packer method
               mock_bundle_configs(server_bundle_name: "webpack-bundle.js")
               # Clear server_bundle_output_path to test manifest behavior
               allow(ReactOnRails).to receive_message_chain("configuration.server_bundle_output_path")
                 .and_return(nil)
               allow(ReactOnRails).to receive_message_chain("configuration.same_bundle_for_client_and_server")
                 .and_return(true)
               mock_bundle_in_manifest("webpack-bundle.js", "webpack/development/webpack-bundle-123456.js")
-              allow(packer).to receive_message_chain("dev_server.running?")
+              allow(Shakapacker).to receive_message_chain("dev_server.running?")
                 .and_return(false)
 
               path = described_class.server_bundle_js_file_path
@@ -340,15 +340,15 @@ def mock_dev_server_running
 
           context "with server file in the manifest, used for client", packer_type.to_sym do
             it "returns the correct path hashed server path" do
-              packer = ::Shakapacker
+              # Use Shakapacker directly instead of packer method
               mock_bundle_configs(rsc_bundle_name: "webpack-bundle.js")
               # Clear server_bundle_output_path to test manifest behavior
               allow(ReactOnRails).to receive_message_chain("configuration.server_bundle_output_path")
                 .and_return(nil)
               allow(ReactOnRails).to receive_message_chain("configuration.same_bundle_for_client_and_server")
                 .and_return(true)
               mock_bundle_in_manifest("webpack-bundle.js", "webpack/development/webpack-bundle-123456.js")
-              allow(packer).to receive_message_chain("dev_server.running?")
+              allow(Shakapacker).to receive_message_chain("dev_server.running?")
                 .and_return(false)
 
               path = described_class.rsc_bundle_js_file_path