Implement `ask' recipe keyword

features/recipes/ask.feature

@@ -0,0 +1,22 @@
+Feature: `ask' recipe keyword
+
+  Scenario: prompts user with a list of choices on standard output
+    Given a recipe with:
+      """
+      task :ask_letter do
+        letter = ask 'Which letter?', %w[A B]
+
+        echo letter
+      end
+      """
+    When I execute the recipe interactively
+    And I type "1"
+    Then the output must contain:
+      """
+      Which letter?
+      0: A
+      1: B
+      Choice:
+      B
+      """
+    And the exit status must be 0

features/steps/recipe_steps.rb

@@ -10,3 +10,7 @@ When(/^I successfully execute the recipe$/) do
   step 'I execute the recipe'
   assert_exit_status(0)
 end
+
+When(/^I execute the recipe interactively$/) do
+  run_interactive('producer recipe.rb')
+end