Improve CLI API related to standard output

lib/producer/core/cli.rb

@@ -3,11 +3,11 @@ module Producer
     class CLI
       USAGE = "Usage: #{File.basename $0} recipe_file"
 
-      attr_reader :arguments
+      attr_reader :arguments, :stdout
 
-      def initialize(arguments, stdout = $stdout)
+      def initialize(arguments, stdout: $stdout)
-        @stdout     = stdout
         @arguments  = arguments
+        @stdout     = stdout
       end
 
       def run!

spec/producer/core/cli_spec.rb

@@ -7,11 +7,15 @@ module Producer::Core
 
     let(:recipe_file) { fixture_path_for 'recipes/empty.rb' }
     let(:arguments)   { [recipe_file] }
-    subject(:cli)     { CLI.new(arguments) }
+    let(:stdout)      { StringIO.new }
+
+    subject(:cli)     { CLI.new(arguments, stdout: stdout) }
 
     describe '#initialize' do
+      subject(:cli) { CLI.new(arguments) }
+
       it 'assigns $stdout as the default standard output' do
-        expect(cli.instance_eval { @stdout }).to be $stdout
+        expect(cli.stdout).to be $stdout
       end
     end
 
@@ -21,6 +25,12 @@ module Producer::Core
       end
     end
 
+    describe '#stdout' do
+      it 'returns the assigned standard output' do
+        expect(cli.stdout).to be stdout
+      end
+    end
+
     describe '#run!' do
       it 'checks the arguments' do
         expect(cli).to receive :check_arguments!
@@ -43,8 +53,6 @@ module Producer::Core
 
       context 'when recipe argument is missing' do
         let(:arguments) { [] }
-        let(:stdout)    { StringIO.new }
-        subject(:cli)   { CLI.new(arguments, stdout) }
 
         it 'exits with a return status of 64' do
           expect { cli.check_arguments! }.to raise_error(SystemExit) { |e|