adding a test case for custom locking

activerecord/test/cases/custom_locking_test.rb

+require "cases/helper"
+require 'models/person'
+
+module ActiveRecord
+  class CustomLockingTest < ActiveRecord::TestCase
+    fixtures :people
+
+    def test_custom_lock
+      if current_adapter?(:MysqlAdapter, :Mysql2Adapter)
+        assert_match 'SHARE MODE', Person.lock('LOCK IN SHARE MODE').to_sql
+        assert_sql(/LOCK IN SHARE MODE/) do
+          Person.find(1, :lock => 'LOCK IN SHARE MODE')
+        end
+      end
+    end
+  end
+end