test: fill coverage gaps in PortSelector and procfile_port

- Assert webpack defaults to 3035 when only PORT is set
- Assert rails defaults to 3000 when only SHAKAPACKER_DEV_SERVER_PORT is set
- Assert no port probing in both single-env-var cases
- Add context for both env vars set simultaneously
- Cover procfile_port dynamic PORT reading and all four combinations

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: ihabadham

react_on_rails/spec/react_on_rails/dev/port_selector_spec.rb

@@ -69,6 +69,11 @@
         expect(result[:rails]).to eq(4000)
       end
 
+      it "defaults webpack to 3035 when SHAKAPACKER_DEV_SERVER_PORT is not set" do
+        result = described_class.select_ports
+        expect(result[:webpack]).to eq(3035)
+      end
+
       it "does not probe for free ports" do
         expect(described_class).not_to receive(:port_available?)
         described_class.select_ports
@@ -87,6 +92,39 @@
         result = described_class.select_ports
         expect(result[:webpack]).to eq(4035)
       end
+
+      it "defaults Rails to 3000 when PORT is not set" do
+        result = described_class.select_ports
+        expect(result[:rails]).to eq(3000)
+      end
+
+      it "does not probe for free ports" do
+        expect(described_class).not_to receive(:port_available?)
+        described_class.select_ports
+      end
+    end
+
+    context "when both PORT and SHAKAPACKER_DEV_SERVER_PORT are set" do
+      around do |example|
+        old_port = ENV.fetch("PORT", nil)
+        old_wp   = ENV.fetch("SHAKAPACKER_DEV_SERVER_PORT", nil)
+        ENV["PORT"] = "4000"
+        ENV["SHAKAPACKER_DEV_SERVER_PORT"] = "4035"
+        example.run
+        ENV["PORT"] = old_port
+        ENV["SHAKAPACKER_DEV_SERVER_PORT"] = old_wp
+      end
+
+      it "returns both explicit ports" do
+        result = described_class.select_ports
+        expect(result[:rails]).to eq(4000)
+        expect(result[:webpack]).to eq(4035)
+      end
+
+      it "does not probe for free ports" do
+        expect(described_class).not_to receive(:port_available?)
+        described_class.select_ports
+      end
     end
 
     context "when no port is available within max attempts" do

react_on_rails/spec/react_on_rails/dev/server_manager_spec.rb

@@ -302,6 +302,28 @@ def mock_system_calls
     end
   end
 
+  describe ".procfile_port" do
+    after { ENV.delete("PORT") }
+
+    it "returns 3000 for Procfile.dev when PORT is unset" do
+      expect(described_class.send(:procfile_port, "Procfile.dev")).to eq(3000)
+    end
+
+    it "returns 3001 for Procfile.dev-prod-assets when PORT is unset" do
+      expect(described_class.send(:procfile_port, "Procfile.dev-prod-assets")).to eq(3001)
+    end
+
+    it "returns the auto-detected port for Procfile.dev when PORT is set" do
+      ENV["PORT"] = "3001"
+      expect(described_class.send(:procfile_port, "Procfile.dev")).to eq(3001)
+    end
+
+    it "returns the PORT value for Procfile.dev-prod-assets when PORT is set" do
+      ENV["PORT"] = "4000"
+      expect(described_class.send(:procfile_port, "Procfile.dev-prod-assets")).to eq(4000)
+    end
+  end
+
   describe ".show_help" do
     it "displays help information" do
       expect { described_class.show_help }.to output(%r{Usage: bin/dev \[command\]}).to_stdout_from_any_process