Emit item promotion in case literal array has only one item

Closes #113

Changelog.md

@@ -2,6 +2,7 @@
 
 Changes:
 
+* Add mutation from [item] to item
 * Add mutation from #reverse_each to #each
 * Add mutation from #reverse_map to #each, #map
 * Add mutation from #map to #each

config/flay.yml

@@ -1,3 +1,3 @@
 ---
 threshold: 18
-total_score: 791
+total_score: 794

lib/mutant/mutator/node/literal/array.rb

@@ -21,6 +21,9 @@ module Mutant
             emit_nil
             emit_self
             mutate_body
+            if children.one?
+              emit(children.first)
+            end
           end
 
           # Mutate body

spec/unit/mutant/mutator/node/literal/array_spec.rb

@@ -3,27 +3,45 @@
 require 'spec_helper'
 
 describe Mutant::Mutator::Node::Literal, 'array' do
-  let(:source) { '[true, false]' }
 
-  let(:mutations) do
-    mutations = []
+  context 'on one item' do
+    let(:source) { '[true]' }
 
-    # Literal replaced with nil
-    mutations << 'nil'
+    let(:mutations) do
+      mutations = []
+      mutations << 'nil'
+      mutations << 'true'
+      mutations << '[false]'
+      mutations << '[nil]'
+      mutations << '[]'
+    end
 
-    # Mutation of each element in array
-    mutations << '[nil, false]'
-    mutations << '[false, false]'
-    mutations << '[true, nil]'
-    mutations << '[true, true]'
-
-    # Remove each element of array once
-    mutations << '[true]'
-    mutations << '[false]'
-
-    # Empty array
-    mutations << '[]'
+    it_should_behave_like 'a mutator'
   end
 
-  it_should_behave_like 'a mutator'
+  context 'on arrays with more than one item' do
+    let(:source) { '[true, false]' }
+
+    let(:mutations) do
+      mutations = []
+
+      # Literal replaced with nil
+      mutations << 'nil'
+
+      # Mutation of each element in array
+      mutations << '[nil, false]'
+      mutations << '[false, false]'
+      mutations << '[true, nil]'
+      mutations << '[true, true]'
+
+      # Remove each element of array once
+      mutations << '[true]'
+      mutations << '[false]'
+
+      # Empty array
+      mutations << '[]'
+    end
+
+    it_should_behave_like 'a mutator'
+  end
 end