Make optional the required argument in have_db_index(...).unique

NEWS.md

@@ -1,5 +1,8 @@
 # HEAD
 
+* Change `have_db_index(...).unique(unique)` so that the `unique` argument
+  is optional, allowing for the shorter `have_db_index(...).unique` syntax.
+
 * Association matchers now test that the model being referred to (either
   implicitly or explicitly, using `:class_name`) actually exists.
 

lib/shoulda/matchers/active_record/have_db_index_matcher.rb

@@ -27,7 +27,7 @@ module Shoulda # :nodoc:
           @options = {}
         end
 
-        def unique(unique)
+        def unique(unique = true)
           @options[:unique] = unique
           self
         end

spec/shoulda/matchers/active_record/have_db_index_matcher_spec.rb

@@ -52,6 +52,10 @@ describe Shoulda::Matchers::ActiveRecord::HaveDbIndexMatcher do
     expect(have_db_index(:user_id).unique(true).description).to match(/a unique index/)
   end
 
+  it 'describes a unique index as unique when no argument is given' do
+    expect(have_db_index(:user_id).unique.description).to match(/a unique index/)
+  end
+
   it 'describes a non-unique index as non-unique' do
     expect(have_db_index(:user_id).unique(false).description).to match(/a non-unique index/)
   end