Strange behavior with 3.1 activerecord tests

I think this is strange (at least):

in test/models/topic.rb line 52
Topic class declares:

serialize :content

But after running ARCONN=sqlite3 ruby -Itest test/cases/finder_test.rb
I found this in the test/fixtures/fixture_database.sqlite3 database

select content from topics;

Have a nice day
Have a nice day
I'm a troll
Why not?

I would expect to have YAML in content column instead of plain text.