Implement `echo' task action

spec/producer/core/actions/echo_spec.rb

@@ -0,0 +1,21 @@
+require 'spec_helper'
+
+module Producer::Core
+  describe Actions::Echo do
+    let(:env)       { Env.new }
+    let(:text)      { 'hello' }
+    subject(:echo)  { Actions::Echo.new(env, text) }
+
+    describe '#apply' do
+      before do
+        env.output = StringIO.new
+      end
+
+      it 'outputs the string given as argument through env.output' do
+        expect(env).to receive(:output).with(text)
+        echo.apply
+      end
+    end
+  end
+end
+

spec/producer/core/task/dsl_spec.rb

@@ -6,7 +6,7 @@ module Producer::Core
     let(:env)     { double('env') }
     subject(:dsl) { Task::DSL.new &block }
 
-    %w[sh].each do |action|
+    %w[echo sh].each do |action|
       it "has `#{action}' action defined" do
         expect(dsl).to respond_to action.to_sym
       end