Rails tests fail in Ruby 1.9.1

This is because ActiveSupport::TestCase line 10 pulls in Test::Unit::TestCase. This file does not exist in Ruby 1.9.1.

Reproduce steps:

# Create skeleton
rails foobar
cd foobar
touch db/schema.rb

# Put this in test/unit/foo_test.rb:
require File.dirname(__FILE__) << '/../test_helper'

class FooTest < ActiveSupport::TestCase
        def test_true
                assert true
        end
end

# Run the fake test
ruby191 /usr/bin/rake

You should see a MissingSourceFile error.