Summary:

Updated a rails app from 3.0.3 to 3.0.4 today
and discovered I could no longer hit breakpoints set within tests.
Attached, you'll find a simple project which duplicates this behavior.

I'm not sure if this is particularly a regression in rails,
but I don't see this behavior when using rails 3.0.3 with this project

To Reproduce the Issue:

Blow out the attached tarball and cd into the foo directory, run the following commands:

rake db:reset
bundle install
rake test

Expected Behavior:

A debugger statement w/in the FooTest should be hit and opened in rdb with output like the following:

rheflin@elitethis:~/src/foo$ rake test
(in /home/rheflin/src/bs)
Loaded suite /home/rheflin/.rvm/gems/ruby-1.9.2-p136/gems/rake-0.8.7/lib/rake/rake_test_loader
Started
[2, 11] in test/unit/foo_test.rb
   2  
   3  class FooTest < ActiveSupport::TestCase
   4    # Replace this with your real tests.
   5    test "the truth" do
   6      debugger
=> 7      assert false
   8    end
   9  end
test/unit/foo_test.rb:7
assert false
(rdb:1)

Actual Behavior:

What actually happens is the breakpoint gets skipped and the test fails.

rheflin@elitethis:~/src/foo$ rake test
(in /home/rheflin/src/foo)
Loaded suite /home/rheflin/.rvm/gems/ruby-1.9.2-p136/gems/rake-0.8.7/lib/rake/rake_test_loader
Started
F
Finished in 0.265451 seconds.

  1) Failure:
test_the_truth(FooTest) [test/unit/foo_test.rb:7]:
Failed assertion, no message given.

1 tests, 1 assertions, 1 failures, 0 errors, 0 skips

Test run options: --seed 36151
Errors running test:units!
rheflin@elitethis:~/src/foo$

Workaround

To get the breakpoint to trigger (as it did in 3.0.3) explicitly add require 'ruby-debug' to the test/test_helper.rb file so its contents match the following:

--- modified test/test_helper.rb

ENV["RAILS_ENV"] = "test"
require File.expand_path('../../config/environment', __FILE__)
require 'rails/test_help'
require 'ruby-debug'

class ActiveSupport::TestCase
  # Setup all fixtures in test/fixtures/*.(yml|csv) for all tests in alphabetical order.
  #
  # Note: You'll currently still have to declare fixtures explicitly in integration tests
  # -- they do not yet inherit this setting
  fixtures :all

  # Add more helper methods to be used by all tests here...
end

Then the breakpoint will be hit and you should drop into the debugger:

rheflin@elitethis:~/src/foo$ rake test
(in /home/rheflin/src/bs)
Loaded suite /home/rheflin/.rvm/gems/ruby-1.9.2-p136/gems/rake-0.8.7/lib/rake/rake_test_loader
Started
[2, 11] in test/unit/foo_test.rb
   2  
   3  class FooTest < ActiveSupport::TestCase
   4    # Replace this with your real tests.
   5    test "the truth" do
   6      debugger
=> 7      assert false
   8    end
   9  end
test/unit/foo_test.rb:7
assert false
(rdb:1)

My Environment details (in case they're needed):
OS: Ubuntu Linux 10.10 (maverick)
Arch: x86_64
Ruby: 1.9.2p136 (built by rvm 1.2.6)

I'll be happy to provide more information if needed, let me know.