Silence warning from MySQL::Error object in test

When running Active Record MySQL test, this warning is printed in the
console:

    warning: instance variable errno not initialized

It turns out that this is a warning from `mysql` gem in MySQL::Error
object. However, since the `mysql` gem is no longer maintained, and
there won't be a newer version, it make sense for us to just silence
this warning to make the output cleaner.

1 files changed, 3 insertions, 1 deletions

diff --git a/activerecord/test/cases/disconnected_test.rb b/activerecord/test/cases/disconnected_test.rb
index 55f0e51717..c25089a420 100644
--- a/activerecord/test/cases/disconnected_test.rb
+++ b/activerecord/test/cases/disconnected_test.rb
@@ -21,7 +21,9 @@ class TestDisconnectedAdapter < ActiveRecord::TestCase
       @connection.execute "SELECT count(*) from products"
       @connection.disconnect!
       assert_raises(ActiveRecord::StatementInvalid) do
-        @connection.execute "SELECT count(*) from products"
+        silence_warnings do
+          @connection.execute "SELECT count(*) from products"
+        end
       end
     end
   end