Add missing test for p_var_ref

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@67660 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/ruby/test_pattern_matching.rb

@@ -199,6 +199,12 @@ class TestPatternMatching < Test::Unit::TestCase
         a == 1
       end
     end
+
+    assert_syntax_error(%q{
+      case 0
+      in ^a
+      end
+    }, /no such local variable/)
   end
 
   def test_literal_value_pattern