title: Rails ActiveRecord doesn't seem to handle null values correctly in the test enviornment
body: <p>Everything seems to work well in the development and production environments:</p>
  
  <pre>> script/console
  Loading development environment (Rails 2.3.8)
  ruby-1.8.7-p302 > Tape.find(:first, :conditions => "deleted_at is not null").deleted_at.nil?
   => false 
  ruby-1.8.7-p302 > Tape.find(:first, :conditions => "deleted_at is null").deleted_at.nil?
   => true</pre>
  
  <p>So why am I getting the exact opposite results in the test environment?</p>
  
  <pre>> script/console test
  Loading test environment (Rails 2.3.8)
  ruby-1.8.7-p302 > Tape.find(:first, :conditions => "deleted_at is not null").deleted_at.nil?
   => true</pre>
  
  <p>Searching for <code>deleted_at is null</code> never returns any records in the test environment, even when some calls have <code>deleted_at = nil</code> and some have a timestamp there.</p>
  
  <p>Here's a partial readout of the mysql table:</p>
  
  <pre>mysql> describe tapes;
  +-----------------+--------------+------+-----+---------+----------------+
  | Field           | Type         | Null | Key | Default | Extra          |
  +-----------------+--------------+------+-----+---------+----------------+
  | id              | int(11)      | NO   | PRI | NULL    | auto_increment |
  ...
  | deleted_at      | datetime     | YES  |     | NULL    |                |
  +-----------------+--------------+------+-----+---------+----------------+</pre>
  
  <p>Does anyone know what's going on?  Is this a bug?</p>