diff --git a/examples/.gitignore b/examples/.gitignore
index 64fd3c0..2c56460 100644
--- a/examples/.gitignore
+++ b/examples/.gitignore
@@ -1,3 +1,4 @@
-*.wasm
+ruby.wasm
 /rubies
 /build
+/dist
diff --git a/examples/Gemfile.lock b/examples/Gemfile.lock
index c3cac2c..19c35c5 100644
--- a/examples/Gemfile.lock
+++ b/examples/Gemfile.lock
@@ -1,7 +1,7 @@
 PATH
   remote: ../..
   specs:
-    ruby_wasm_ui (0.8.3)
+    ruby_wasm_ui (0.9.0)
       js (~> 2.7)
       listen (~> 3.8)
       puma (~> 6.0)
diff --git a/examples/src/index.html b/examples/src/index.html
index d671269..f0dec56 100644
--- a/examples/src/index.html
+++ b/examples/src/index.html
@@ -5,7 +5,7 @@
     <title>My App</title>
     <script type="module">
       import { DefaultRubyVM } from "https://cdn.jsdelivr.net/npm/@ruby/wasm-wasi@2.7.2/dist/browser/+esm";
-      const response = await fetch("../src.wasm");
+      const response = await fetch("./src.wasm");
       const module = await WebAssembly.compileStreaming(response);
       const { vm } = await DefaultRubyVM(module);
       vm.evalAsync(`
diff --git a/lib/ruby_wasm_ui/cli/command/base.rb b/lib/ruby_wasm_ui/cli/command/base.rb
index 7113e19..6c55a3b 100644
--- a/lib/ruby_wasm_ui/cli/command/base.rb
+++ b/lib/ruby_wasm_ui/cli/command/base.rb
@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 
+require "fileutils"
 require "open3"
 require "bundler/setup"
 require "ruby_wasm"
@@ -74,35 +75,6 @@ def ensure_ruby_wasm
           end
         end
 
-        def update_gitignore(entries_to_add)
-          gitignore_path = ".gitignore"
-
-          # Read existing .gitignore or create new content
-          if File.exist?(gitignore_path)
-            content = File.read(gitignore_path)
-            lines = content.lines.map(&:chomp)
-          else
-            lines = []
-          end
-
-          # Add entries that don't already exist
-          added_entries = []
-          entries_to_add.each do |entry|
-            unless lines.include?(entry)
-              lines << entry
-              added_entries << entry
-            end
-          end
-
-          # Write back to .gitignore
-          File.write(gitignore_path, lines.join("\n") + "\n")
-          if added_entries.any?
-            log_info("Added to .gitignore: #{added_entries.join(', ')}")
-          else
-            log_info("No new entries added to .gitignore (all entries already exist)")
-          end
-        end
-
         protected
 
         def log_info(message)
@@ -168,6 +140,52 @@ def build_ruby_wasm(ruby_version_str)
           cli = RubyWasm::CLI.new(stdout: $stdout, stderr: $stderr)
           cli.run(command)
         end
+
+        def ensure_dist_directory
+          unless Dir.exist?("dist")
+            Dir.mkdir("dist")
+            log_info("Created dist directory")
+          end
+        end
+
+        def copy_non_ruby_files
+          log_info("Copying non-Ruby files from src to dist...")
+
+          copied_files = []
+          Dir.glob("src/**/*").each do |src_path|
+            next if File.directory?(src_path)
+            next if src_path.end_with?(".rb")
+
+            # Get relative path from src directory
+            relative_path = src_path.sub(/^src\//, "")
+            dest_path = File.join("dist", relative_path)
+
+            # Create destination directory if needed
+            dest_dir = File.dirname(dest_path)
+            FileUtils.mkdir_p(dest_dir) unless Dir.exist?(dest_dir)
+
+            # Copy file
+            FileUtils.cp(src_path, dest_path)
+            copied_files << relative_path
+          end
+
+          if copied_files.any?
+            log_success("✓ Copied #{copied_files.size} file(s): #{copied_files.join(', ')}")
+          else
+            log_info("No non-Ruby files to copy")
+          end
+        end
+
+        def pack_wasm(exit_on_error: true, log_prefix: "Packing")
+          command = "bundle exec rbwasm pack ruby.wasm --dir ./src::./src -o dist/src.wasm"
+          log_info("#{log_prefix}: #{command}")
+
+          success = run_command(command, exit_on_error: exit_on_error)
+          if success
+            log_success("✓ Pack completed")
+          end
+          success
+        end
       end
     end
   end
diff --git a/lib/ruby_wasm_ui/cli/command/dev.rb b/lib/ruby_wasm_ui/cli/command/dev.rb
index 3b0be3e..280e502 100644
--- a/lib/ruby_wasm_ui/cli/command/dev.rb
+++ b/lib/ruby_wasm_ui/cli/command/dev.rb
@@ -19,6 +19,7 @@ def run(_argv)
           puts ""
 
           ensure_src_directory
+          ensure_ruby_wasm
 
           # Initial build
           log_info("Performing initial build...")
@@ -76,11 +77,11 @@ def cleanup
         end
 
         def build
-          command = "bundle exec rbwasm pack ruby.wasm --dir ./src::./src -o src.wasm"
-          log_info("Building: #{command}")
+          ensure_dist_directory
 
-          success = run_command(command, exit_on_error: false)
+          success = pack_wasm(exit_on_error: false, log_prefix: "Building")
           if success
+            copy_non_ruby_files
             log_success("✓ Build completed")
           else
             log_error("Build failed")
@@ -132,11 +133,11 @@ def start_server
           # Static file server application
           static_app = lambda do |env|
             path = env["PATH_INFO"]
-            if path == "/"
-              file_path = File.join(Dir.pwd, "src", "index.html")
-            else
-              file_path = File.join(Dir.pwd, path)
-            end
+            # Remove leading slash and handle root path
+            relative_path = path == "/" ? "index.html" : path.sub(/^\//, "")
+
+            # Serve files from dist directory
+            file_path = File.join(Dir.pwd, "dist", relative_path)
 
             if File.exist?(file_path) && File.file?(file_path)
               content_type = Rack::Mime.mime_type(File.extname(file_path), "text/html")
@@ -187,7 +188,7 @@ def start_server
             # Open browser after a short delay to ensure server is ready
             Thread.new do
               sleep 1
-              open_browser("http://localhost:#{port}/src/index.html")
+              open_browser("http://localhost:#{port}/index.html")
             end
 
             Rack::Handler::Puma.run(app, Port: port, Host: "0.0.0.0")
diff --git a/lib/ruby_wasm_ui/cli/command/pack.rb b/lib/ruby_wasm_ui/cli/command/pack.rb
index b2c313a..4f2f4cf 100644
--- a/lib/ruby_wasm_ui/cli/command/pack.rb
+++ b/lib/ruby_wasm_ui/cli/command/pack.rb
@@ -16,19 +16,19 @@ def run(_argv)
 
           ensure_src_directory
           ensure_ruby_wasm
+          ensure_dist_directory
 
           # Pack WASM file
           pack
+
+          # Copy non-Ruby files from src to dist
+          copy_non_ruby_files
         end
 
         private
 
         def pack
-          command = "bundle exec rbwasm pack ruby.wasm --dir ./src::./src -o src.wasm"
-          log_info("Packing: #{command}")
-
-          run_command(command)
-          log_success("✓ Pack completed")
+          pack_wasm(exit_on_error: true, log_prefix: 'Packing')
         end
       end
     end
diff --git a/lib/ruby_wasm_ui/cli/command/setup.rb b/lib/ruby_wasm_ui/cli/command/setup.rb
index d750df4..e5d4784 100644
--- a/lib/ruby_wasm_ui/cli/command/setup.rb
+++ b/lib/ruby_wasm_ui/cli/command/setup.rb
@@ -32,7 +32,7 @@ def run(_argv)
           # Update .gitignore
           puts ""
           log_info("Step 3/4: Updating .gitignore...")
-          update_gitignore(["*.wasm", "/rubies", "/build"])
+          update_gitignore(["ruby.wasm", "/rubies", "/build", "/dist"])
           log_success("✓ .gitignore updated")
 
           # Create initial files
@@ -46,6 +46,35 @@ def run(_argv)
 
         private
 
+        def update_gitignore(entries_to_add)
+          gitignore_path = ".gitignore"
+
+          # Read existing .gitignore or create new content
+          if File.exist?(gitignore_path)
+            content = File.read(gitignore_path)
+            lines = content.lines.map(&:chomp)
+          else
+            lines = []
+          end
+
+          # Add entries that don't already exist
+          added_entries = []
+          entries_to_add.each do |entry|
+            unless lines.include?(entry)
+              lines << entry
+              added_entries << entry
+            end
+          end
+
+          # Write back to .gitignore
+          File.write(gitignore_path, lines.join("\n") + "\n")
+          if added_entries.any?
+            log_info("Added to .gitignore: #{added_entries.join(', ')}")
+          else
+            log_info("No new entries added to .gitignore (all entries already exist)")
+          end
+        end
+
         def create_initial_files
           # Skip if src directory exists
           if Dir.exist?("src")
@@ -76,7 +105,7 @@ def create_initial_files
                 <title>My App</title>
                 <script type="module">
                   import { DefaultRubyVM } from "https://cdn.jsdelivr.net/npm/@ruby/wasm-wasi@2.7.2/dist/browser/+esm";
-                  const response = await fetch("../src.wasm");
+                  const response = await fetch("./src.wasm");
                   const module = await WebAssembly.compileStreaming(response);
                   const { vm } = await DefaultRubyVM(module);
                   vm.evalAsync(`
diff --git a/spec/ruby_wasm_ui/cli/command/base_spec.rb b/spec/ruby_wasm_ui/cli/command/base_spec.rb
index cd749f4..5baa211 100644
--- a/spec/ruby_wasm_ui/cli/command/base_spec.rb
+++ b/spec/ruby_wasm_ui/cli/command/base_spec.rb
@@ -13,63 +13,6 @@
     end
   end
 
-  describe '#update_gitignore' do
-    let(:temp_dir) { Dir.mktmpdir }
-    let(:original_dir) { Dir.pwd }
-
-    around do |example|
-      Dir.chdir(temp_dir) do
-        example.run
-      end
-    ensure
-      FileUtils.rm_rf(temp_dir) if Dir.exist?(temp_dir)
-    end
-
-    context 'when .gitignore does not exist' do
-      it 'creates .gitignore with new entries' do
-        base_instance.send(:update_gitignore, ['*.wasm', '/rubies'])
-        content = File.read('.gitignore')
-        expect(content).to include('*.wasm')
-        expect(content).to include('/rubies')
-      end
-    end
-
-    context 'when .gitignore exists' do
-      before do
-        File.write('.gitignore', "node_modules/\n*.log\n")
-      end
-
-      it 'adds new entries to existing .gitignore' do
-        base_instance.send(:update_gitignore, ['*.wasm', '/rubies'])
-        content = File.read('.gitignore')
-        expect(content).to include('node_modules/')
-        expect(content).to include('*.log')
-        expect(content).to include('*.wasm')
-        expect(content).to include('/rubies')
-      end
-
-      it 'does not add duplicate entries' do
-        File.write('.gitignore', "*.wasm\n")
-        base_instance.send(:update_gitignore, ['*.wasm', '/rubies'])
-        content = File.read('.gitignore')
-        expect(content.scan(/^\*\.wasm$/).count).to eq(1)
-      end
-
-      it 'outputs message when entries are added' do
-        expect { base_instance.send(:update_gitignore, ['*.wasm']) }.to output(
-          /Added to .gitignore: \*\.wasm/
-        ).to_stdout
-      end
-
-      it 'outputs message when no entries are added' do
-        File.write('.gitignore', "*.wasm\n")
-        expect { base_instance.send(:update_gitignore, ['*.wasm']) }.to output(
-          /No new entries added to .gitignore/
-        ).to_stdout
-      end
-    end
-  end
-
   describe '#run_command' do
     context 'when command succeeds' do
       it 'executes the command and outputs stdout' do
@@ -355,4 +298,206 @@
       base_instance.send(:build_ruby_wasm, '3.4')
     end
   end
+
+  describe '#ensure_dist_directory' do
+    let(:temp_dir) { Dir.mktmpdir }
+    let(:original_dir) { Dir.pwd }
+
+    around do |example|
+      Dir.chdir(temp_dir) do
+        example.run
+      end
+    ensure
+      FileUtils.rm_rf(temp_dir) if Dir.exist?(temp_dir)
+    end
+
+    context 'when dist directory does not exist' do
+      it 'creates dist directory' do
+        expect(Dir.exist?('dist')).to be false
+        base_instance.send(:ensure_dist_directory)
+        expect(Dir.exist?('dist')).to be true
+      end
+
+      it 'outputs creation message' do
+        expect { base_instance.send(:ensure_dist_directory) }.to output(
+          /Created dist directory/
+        ).to_stdout
+      end
+    end
+
+    context 'when dist directory already exists' do
+      before do
+        FileUtils.mkdir_p('dist')
+      end
+
+      it 'does not create dist directory again' do
+        expect(Dir).not_to receive(:mkdir)
+        base_instance.send(:ensure_dist_directory)
+      end
+
+      it 'does not output creation message' do
+        expect { base_instance.send(:ensure_dist_directory) }.not_to output(
+          /Created dist directory/
+        ).to_stdout
+      end
+    end
+  end
+
+  describe '#copy_non_ruby_files' do
+    let(:temp_dir) { Dir.mktmpdir }
+    let(:original_dir) { Dir.pwd }
+
+    around do |example|
+      Dir.chdir(temp_dir) do
+        example.run
+      end
+    ensure
+      FileUtils.rm_rf(temp_dir) if Dir.exist?(temp_dir)
+    end
+
+    context 'when non-Ruby files exist' do
+      before do
+        FileUtils.mkdir_p('src')
+        File.write('src/index.html', '<html></html>')
+        File.write('src/style.css', 'body {}')
+        File.write('src/app.rb', 'puts "hello"')
+        FileUtils.mkdir_p('src/subdir')
+        File.write('src/subdir/script.js', 'console.log("test")')
+      end
+
+      it 'copies HTML files to dist' do
+        base_instance.send(:copy_non_ruby_files)
+        expect(File.exist?('dist/index.html')).to be true
+        expect(File.read('dist/index.html')).to eq('<html></html>')
+      end
+
+      it 'copies CSS files to dist' do
+        base_instance.send(:copy_non_ruby_files)
+        expect(File.exist?('dist/style.css')).to be true
+        expect(File.read('dist/style.css')).to eq('body {}')
+      end
+
+      it 'does not copy Ruby files' do
+        base_instance.send(:copy_non_ruby_files)
+        expect(File.exist?('dist/app.rb')).to be false
+      end
+
+      it 'preserves directory structure' do
+        base_instance.send(:copy_non_ruby_files)
+        expect(File.exist?('dist/subdir/script.js')).to be true
+        expect(File.read('dist/subdir/script.js')).to eq('console.log("test")')
+      end
+
+      it 'outputs success message with copied files' do
+        expect { base_instance.send(:copy_non_ruby_files) }.to output(
+          /Copied.*file\(s\)/
+        ).to_stdout
+      end
+    end
+
+    context 'when no non-Ruby files exist' do
+      before do
+        FileUtils.mkdir_p('src')
+        File.write('src/app.rb', 'puts "hello"')
+      end
+
+      it 'outputs no files message' do
+        expect { base_instance.send(:copy_non_ruby_files) }.to output(
+          /No non-Ruby files to copy/
+        ).to_stdout
+      end
+    end
+  end
+
+  describe '#pack_wasm' do
+    let(:temp_dir) { Dir.mktmpdir }
+    let(:original_dir) { Dir.pwd }
+
+    around do |example|
+      Dir.chdir(temp_dir) do
+        example.run
+      end
+    ensure
+      FileUtils.rm_rf(temp_dir) if Dir.exist?(temp_dir)
+    end
+
+    before do
+      FileUtils.mkdir_p('src')
+      FileUtils.touch('ruby.wasm')
+    end
+
+    context 'when command succeeds' do
+      before do
+        allow(base_instance).to receive(:run_command).and_return(true)
+      end
+
+      it 'executes rbwasm pack command via run_command' do
+        expect(base_instance).to receive(:run_command).with(
+          'bundle exec rbwasm pack ruby.wasm --dir ./src::./src -o dist/src.wasm',
+          exit_on_error: true
+        )
+        base_instance.send(:pack_wasm)
+      end
+
+      it 'outputs pack message with default prefix' do
+        expect { base_instance.send(:pack_wasm) }.to output(
+          /Packing: bundle exec rbwasm pack/
+        ).to_stdout
+      end
+
+      it 'outputs pack message with custom prefix' do
+        expect { base_instance.send(:pack_wasm, log_prefix: 'Building') }.to output(
+          /Building: bundle exec rbwasm pack/
+        ).to_stdout
+      end
+
+      it 'outputs success message' do
+        expect { base_instance.send(:pack_wasm) }.to output(
+          /Pack completed/
+        ).to_stdout
+      end
+
+      it 'returns true' do
+        result = base_instance.send(:pack_wasm)
+        expect(result).to be true
+      end
+    end
+
+    context 'when command fails' do
+      before do
+        allow(base_instance).to receive(:run_command).and_raise(SystemExit.new(1))
+      end
+
+      it 'outputs error message and exits by default' do
+        expect { base_instance.send(:pack_wasm) }.to raise_error(SystemExit)
+      end
+
+      it 'exits with status 1' do
+        expect { base_instance.send(:pack_wasm) }.to raise_error(SystemExit) do |error|
+          expect(error.status).to eq(1)
+        end
+      end
+
+      context 'when exit_on_error is false' do
+        before do
+          allow(base_instance).to receive(:run_command).and_return(false)
+        end
+
+        it 'does not raise error' do
+          expect { base_instance.send(:pack_wasm, exit_on_error: false) }.not_to raise_error
+        end
+
+        it 'returns false' do
+          result = base_instance.send(:pack_wasm, exit_on_error: false)
+          expect(result).to be false
+        end
+
+        it 'does not output success message when command fails' do
+          expect { base_instance.send(:pack_wasm, exit_on_error: false) }.not_to output(
+            /Pack completed/
+          ).to_stdout
+        end
+      end
+    end
+  end
 end
diff --git a/spec/ruby_wasm_ui/cli/command/dev_spec.rb b/spec/ruby_wasm_ui/cli/command/dev_spec.rb
index edcca7e..8e99122 100644
--- a/spec/ruby_wasm_ui/cli/command/dev_spec.rb
+++ b/spec/ruby_wasm_ui/cli/command/dev_spec.rb
@@ -55,9 +55,28 @@
       end
     end
 
+    context 'when src directory exists but ruby.wasm does not exist' do
+      before do
+        FileUtils.mkdir_p('src')
+      end
+
+      it 'outputs error message and exits' do
+        expect { dev_instance.run([]) }.to output(
+          /ruby.wasm not found. Please run 'ruby-wasm-ui setup' first./
+        ).to_stdout.and raise_error(SystemExit)
+      end
+
+      it 'exits with status 1' do
+        expect { dev_instance.run([]) }.to raise_error(SystemExit) do |error|
+          expect(error.status).to eq(1)
+        end
+      end
+    end
+
     context 'when src directory exists' do
       before do
         FileUtils.mkdir_p('src')
+        FileUtils.touch('ruby.wasm')
       end
 
       it 'outputs starting message' do
@@ -116,6 +135,7 @@
   describe '#build' do
     before do
       FileUtils.mkdir_p('src')
+      FileUtils.touch('ruby.wasm')
     end
 
     context 'when command succeeds' do
@@ -123,11 +143,9 @@
         allow(dev_instance).to receive(:run_command).and_return(true)
       end
 
-      it 'executes rbwasm pack command via run_command' do
-        expect(dev_instance).to receive(:run_command).with(
-          'bundle exec rbwasm pack ruby.wasm --dir ./src::./src -o src.wasm',
-          exit_on_error: false
-        )
+      it 'calls pack_wasm with Building log_prefix' do
+        expect(dev_instance).to receive(:pack_wasm).with(exit_on_error: false, log_prefix: 'Building').and_return(true)
+        allow(dev_instance).to receive(:copy_non_ruby_files)
         dev_instance.send(:build)
       end
 
@@ -137,6 +155,12 @@
         ).to_stdout
       end
 
+      it 'calls copy_non_ruby_files when build succeeds' do
+        allow(dev_instance).to receive(:pack_wasm).and_return(true)
+        expect(dev_instance).to receive(:copy_non_ruby_files)
+        dev_instance.send(:build)
+      end
+
       it 'outputs success message' do
         expect { dev_instance.send(:build) }.to output(
           /Build completed/
@@ -154,6 +178,12 @@
         allow(dev_instance).to receive(:run_command).and_return(false)
       end
 
+      it 'does not call copy_non_ruby_files when build fails' do
+        allow(dev_instance).to receive(:pack_wasm).and_return(false)
+        expect(dev_instance).not_to receive(:copy_non_ruby_files)
+        dev_instance.send(:build)
+      end
+
       it 'outputs error message' do
         expect { dev_instance.send(:build) }.to output(
           /Build failed/
@@ -306,7 +336,7 @@ def self.run(app, options = {})
           instance_double(Thread)
         end
 
-        expect(dev_instance).to receive(:open_browser).with('http://localhost:8080/src/index.html').and_return(nil)
+        expect(dev_instance).to receive(:open_browser).with('http://localhost:8080/index.html').and_return(nil)
 
         dev_instance.send(:start_server)
 
@@ -358,8 +388,8 @@ def self.run(app, options = {})
       end
 
       it 'calls open command' do
-        expect(dev_instance).to receive(:system).with('open', 'http://localhost:8080/src/index.html').and_return(true)
-        dev_instance.send(:open_browser, 'http://localhost:8080/src/index.html')
+        expect(dev_instance).to receive(:system).with('open', 'http://localhost:8080/index.html').and_return(true)
+        dev_instance.send(:open_browser, 'http://localhost:8080/index.html')
       end
 
       context 'when system call fails' do
@@ -368,8 +398,8 @@ def self.run(app, options = {})
         end
 
         it 'outputs fallback message' do
-          expect { dev_instance.send(:open_browser, 'http://localhost:8080/src/index.html') }.to output(
-            /Please open http:\/\/localhost:8080\/src\/index.html in your browser/
+          expect { dev_instance.send(:open_browser, 'http://localhost:8080/index.html') }.to output(
+            /Please open http:\/\/localhost:8080\/index.html in your browser/
           ).to_stdout
         end
       end
@@ -381,8 +411,8 @@ def self.run(app, options = {})
       end
 
       it 'calls xdg-open command' do
-        expect(dev_instance).to receive(:system).with('xdg-open', 'http://localhost:8080/src/index.html').and_return(true)
-        dev_instance.send(:open_browser, 'http://localhost:8080/src/index.html')
+        expect(dev_instance).to receive(:system).with('xdg-open', 'http://localhost:8080/index.html').and_return(true)
+        dev_instance.send(:open_browser, 'http://localhost:8080/index.html')
       end
     end
 
@@ -392,8 +422,8 @@ def self.run(app, options = {})
       end
 
       it 'calls start command' do
-        expect(dev_instance).to receive(:system).with('start', 'http://localhost:8080/src/index.html').and_return(true)
-        dev_instance.send(:open_browser, 'http://localhost:8080/src/index.html')
+        expect(dev_instance).to receive(:system).with('start', 'http://localhost:8080/index.html').and_return(true)
+        dev_instance.send(:open_browser, 'http://localhost:8080/index.html')
       end
     end
 
@@ -403,8 +433,8 @@ def self.run(app, options = {})
       end
 
       it 'outputs manual instruction' do
-        expect { dev_instance.send(:open_browser, 'http://localhost:8080/src/index.html') }.to output(
-          /Please open http:\/\/localhost:8080\/src\/index.html in your browser/
+        expect { dev_instance.send(:open_browser, 'http://localhost:8080/index.html') }.to output(
+          /Please open http:\/\/localhost:8080\/index.html in your browser/
         ).to_stdout
       end
     end
diff --git a/spec/ruby_wasm_ui/cli/command/pack_spec.rb b/spec/ruby_wasm_ui/cli/command/pack_spec.rb
index 4937b4e..9efcaca 100644
--- a/spec/ruby_wasm_ui/cli/command/pack_spec.rb
+++ b/spec/ruby_wasm_ui/cli/command/pack_spec.rb
@@ -62,6 +62,7 @@
         FileUtils.mkdir_p('src')
         FileUtils.touch('ruby.wasm')
         allow(pack_instance).to receive(:pack)
+        allow(pack_instance).to receive(:copy_non_ruby_files)
       end
 
       it 'outputs packing message' do
@@ -74,6 +75,11 @@
         expect(pack_instance).to receive(:pack)
         pack_instance.run([])
       end
+
+      it 'calls copy_non_ruby_files method' do
+        expect(pack_instance).to receive(:copy_non_ruby_files)
+        pack_instance.run([])
+      end
     end
   end
 
@@ -88,10 +94,8 @@
         allow(pack_instance).to receive(:run_command).and_return(true)
       end
 
-      it 'executes rbwasm pack command via run_command' do
-        expect(pack_instance).to receive(:run_command).with(
-          'bundle exec rbwasm pack ruby.wasm --dir ./src::./src -o src.wasm'
-        )
+      it 'calls pack_wasm with default parameters' do
+        expect(pack_instance).to receive(:pack_wasm).with(exit_on_error: true, log_prefix: 'Packing').and_return(true)
         pack_instance.send(:pack)
       end
 
diff --git a/spec/ruby_wasm_ui/cli/command/setup_spec.rb b/spec/ruby_wasm_ui/cli/command/setup_spec.rb
index 442b757..1082c44 100644
--- a/spec/ruby_wasm_ui/cli/command/setup_spec.rb
+++ b/spec/ruby_wasm_ui/cli/command/setup_spec.rb
@@ -13,11 +13,20 @@
   end
 
   describe '#run' do
+    let(:temp_dir) { Dir.mktmpdir }
+
+    around do |example|
+      Dir.chdir(temp_dir) do
+        example.run
+      end
+    ensure
+      FileUtils.rm_rf(temp_dir) if Dir.exist?(temp_dir)
+    end
+
     before do
       allow(setup_instance).to receive(:check_ruby_version).and_return(RUBY_VERSION.split('.')[0..1].join('.'))
       allow(setup_instance).to receive(:configure_excluded_gems)
       allow(setup_instance).to receive(:build_ruby_wasm)
-      allow(setup_instance).to receive(:update_gitignore)
       allow(setup_instance).to receive(:create_initial_files)
     end
 
@@ -44,10 +53,12 @@
     end
 
     it 'updates .gitignore with required entries' do
-      expect(setup_instance).to receive(:update_gitignore).with(
-        ['*.wasm', '/rubies', '/build']
-      )
       setup_instance.run([])
+      content = File.read('.gitignore')
+      expect(content).to include('ruby.wasm')
+      expect(content).to include('/rubies')
+      expect(content).to include('/build')
+      expect(content).to include('/dist')
     end
 
     it 'outputs completion message' do
@@ -85,7 +96,6 @@
       it 'does not execute subsequent steps' do
         expect(setup_instance).not_to receive(:configure_excluded_gems)
         expect(setup_instance).not_to receive(:build_ruby_wasm)
-        expect(setup_instance).not_to receive(:update_gitignore)
         expect(setup_instance).not_to receive(:create_initial_files)
         expect { setup_instance.run([]) }.to raise_error(SystemExit)
       end
@@ -97,7 +107,6 @@
         allow(setup_instance).to receive(:check_ruby_version).and_return('3.2')
         allow(setup_instance).to receive(:configure_excluded_gems)
         allow(setup_instance).to receive(:build_ruby_wasm)
-        allow(setup_instance).to receive(:update_gitignore)
         allow(setup_instance).to receive(:create_initial_files)
       end
 
@@ -183,4 +192,60 @@
       end
     end
   end
+
+  describe '#update_gitignore' do
+    let(:temp_dir) { Dir.mktmpdir }
+
+    around do |example|
+      Dir.chdir(temp_dir) do
+        example.run
+      end
+    ensure
+      FileUtils.rm_rf(temp_dir) if Dir.exist?(temp_dir)
+    end
+
+    context 'when .gitignore does not exist' do
+      it 'creates .gitignore with new entries' do
+        setup_instance.send(:update_gitignore, ['*.wasm', '/rubies'])
+        content = File.read('.gitignore')
+        expect(content).to include('*.wasm')
+        expect(content).to include('/rubies')
+      end
+    end
+
+    context 'when .gitignore exists' do
+      before do
+        File.write('.gitignore', "node_modules/\n*.log\n")
+      end
+
+      it 'adds new entries to existing .gitignore' do
+        setup_instance.send(:update_gitignore, ['*.wasm', '/rubies'])
+        content = File.read('.gitignore')
+        expect(content).to include('node_modules/')
+        expect(content).to include('*.log')
+        expect(content).to include('*.wasm')
+        expect(content).to include('/rubies')
+      end
+
+      it 'does not add duplicate entries' do
+        File.write('.gitignore', "*.wasm\n")
+        setup_instance.send(:update_gitignore, ['*.wasm', '/rubies'])
+        content = File.read('.gitignore')
+        expect(content.scan(/^\*\.wasm$/).count).to eq(1)
+      end
+
+      it 'outputs message when entries are added' do
+        expect { setup_instance.send(:update_gitignore, ['*.wasm']) }.to output(
+          /Added to .gitignore: \*\.wasm/
+        ).to_stdout
+      end
+
+      it 'outputs message when no entries are added' do
+        File.write('.gitignore', "*.wasm\n")
+        expect { setup_instance.send(:update_gitignore, ['*.wasm']) }.to output(
+          /No new entries added to .gitignore/
+        ).to_stdout
+      end
+    end
+  end
 end