Fail when `file_append' misses some arguments

lib/producer/core/actions/file_append.rb

@@ -3,6 +3,10 @@ module Producer
     module Actions
       class FileAppend < Action
         def setup
+          if arguments.compact.size != 2
+            fail ArgumentError, '`%s\' action requires 2 arguments' % name
+          end
+
           @path, @content = arguments
         end
 

spec/producer/core/actions/file_append_spec.rb

@@ -12,6 +12,16 @@ module Producer::Core
 
       before { allow(remote_fs).to receive(:file_read).with(path) { content } }
 
+      describe '#setup' do
+        context 'when content is missing' do
+          let(:added_content) { nil }
+
+          it 'raises ArgumentError' do
+            expect { action }.to raise_error ArgumentError
+          end
+        end
+      end
+
       describe '#apply' do
         it 'appends given content to requested file on remote filesystem' do
           expect(remote_fs)