`index_exists?` with `:name` checks specified columns.

[Yves Senn & Matthew Draper]

The column check was embodied in the defaul index name.
If the :name option was used, the specified columns were not verified at all.

Given:

```
assert connection.index_exists?(table_name, :foo_id, :name => :index_testings_on_yo_momma)
```

That index could have been defined on any field, not necessarily on `:foo_id`.

1 files changed, 6 insertions, 0 deletions

diff --git a/activerecord/test/cases/migration/index_test.rb b/activerecord/test/cases/migration/index_test.rb
index 93c3bfae7a..ac932378fd 100644
--- a/activerecord/test/cases/migration/index_test.rb
+++ b/activerecord/test/cases/migration/index_test.rb
@@ -95,6 +95,12 @@ module ActiveRecord
         assert connection.index_exists?(:testings, [:foo, :bar])
       end
 
+      def test_index_exists_with_custom_name_checks_columns
+        connection.add_index :testings, [:foo, :bar], name: "my_index"
+        assert connection.index_exists?(:testings, [:foo, :bar], name: "my_index")
+        assert_not connection.index_exists?(:testings, [:foo], name: "my_index")
+      end
+
       def test_valid_index_options
         assert_raise ArgumentError do
           connection.add_index :testings, :foo, unqiue: true