silent rake test failure--doesn't happen on manual test run

[I. E. Smith-Heisters]

Hi all,

This is kinda weird. I'm working on a plugin. On the same computer
(eg. same gems, ruby, etc.), installed into different apps, it fails
silently in one, but works in the other. The code is identical, since
it's exported through an svn export.

on app a, it works:
---
$ svn up
At revision 1191.
$ rake
(in /home/.../vendor/plugins/acts_as_media_file_manager)
/home/ian/sw/bin/ruby -Ilib:lib "/home/ian/sw/lib/ruby/gems/1.8/gems/
rake-0.8.1/lib/rake/rake_test_loader.rb" "test/
image_processing_test.rb" "test/url_helper_test.rb" "test/
pathname_test.rb" "test/publisher_test.rb" "test/
file_manager_test.rb"
Loaded suite /home/ian/sw/lib/ruby/gems/1.8/gems/rake-0.8.1/lib/rake/
rake_test_loader
Started
.....................................................................................
Finished in 2.32446 seconds.

85 tests, 279 assertions, 0 failures, 0 errors
$
---
on app b, it fails silently:
---
$ svn up
At revision 1191.
$ rake
(in /home/.../vendor/plugins/acts_as_media_file_manager)
/home/ian/sw/bin/ruby -Ilib:lib "/home/ian/sw/lib/ruby/gems/1.8/gems/
rake-0.8.1/lib/rake/rake_test_loader.rb" "test/url_helper_test.rb"
"test/file_manager_test.rb" "test/publisher_test.rb" "test/
pathname_test.rb" "test/image_processing_test.rb"
$
---
but, I can run it manually in app b:
---
$ ruby -r'test/unit' -r'test/unit/ui/console/testrunner' -
e"Dir.glob('test/*_test.rb').each{|f|require f}"
Loaded suite -e
Started
.....................................................................................
Finished in 2.162993 seconds.

85 tests, 277 assertions, 0 failures, 0 errors
$
---
rake -t is unhelpful:
---
$ rake -t
(in /home/.../vendor/plugins/acts_as_media_file_manager)
** Invoke default (first_time)
** Invoke test (first_time)
** Execute test
/home/ian/sw/bin/ruby -Ilib:lib "/home/ian/sw/lib/ruby/gems/1.8/gems/
rake-0.8.1/lib/rake/rake_test_loader.rb" "test/url_helper_test.rb"
"test/file_manager_test.rb" "test/publisher_test.rb" "test/
pathname_test.rb" "test/image_processing_test.rb"
** Execute default
$
---
I'm stumped. Any ideas?

Thanks!
-Ian