rails: `rails console` fails with "`require': cannot load such file -- minitest/unit (LoadError)" with default app on Cygwin

With a fresh install, running rails console gives this error. Rails 3.2.12. Activesupport 3.2.12.

gem uninstall activesupport
gem install activesupport
rails new testapp
cd testapp
rails console

/usr/lib/ruby/gems/1.9.1/gems/activesupport-3.2.12/lib/active_support/dependencies.rb:251:in `require': cannot load such file -- minitest/unit (LoadError)
        from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.2.12/lib/active_support/dependencies.rb:251:in `block in require'
        from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.2.12/lib/active_support/dependencies.rb:236:in `load_dependency'
        from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.2.12/lib/active_support/dependencies.rb:251:in `require'
        from /usr/lib/ruby/1.9.1/test/unit/assertions.rb:1:in `<top (required)>'
        from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.2.12/lib/active_support/dependencies.rb:251:in `require'
        from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.2.12/lib/active_support/dependencies.rb:251:in `block in require'
        from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.2.12/lib/active_support/dependencies.rb:236:in `load_dependency'
        from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.2.12/lib/active_support/dependencies.rb:251:in `require'
        from /usr/lib/ruby/1.9.1/test/unit/testcase.rb:1:in `<top (required)>'
        from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.2.12/lib/active_support/dependencies.rb:251:in `require'
        from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.2.12/lib/active_support/dependencies.rb:251:in `block in require'
        from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.2.12/lib/active_support/dependencies.rb:236:in `load_dependency'
        from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.2.12/lib/active_support/dependencies.rb:251:in `require'
        from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.2.12/lib/active_support/test_case.rb:1:in `<top (required)>'
        from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.2.12/lib/active_support/dependencies.rb:251:in `require'
        from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.2.12/lib/active_support/dependencies.rb:251:in `block in require'
        from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.2.12/lib/active_support/dependencies.rb:236:in `load_dependency'
        from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.2.12/lib/active_support/dependencies.rb:251:in `require'
        from /usr/lib/ruby/gems/1.9.1/gems/railties-3.2.12/lib/rails/console/app.rb:2:in `<top (required)>'
        from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.2.12/lib/active_support/dependencies.rb:251:in `require'
        from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.2.12/lib/active_support/dependencies.rb:251:in `block in require'
        from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.2.12/lib/active_support/dependencies.rb:236:in `load_dependency'
        from /usr/lib/ruby/gems/1.9.1/gems/activesupport-3.2.12/lib/active_support/dependencies.rb:251:in `require'
        from /usr/lib/ruby/gems/1.9.1/gems/railties-3.2.12/lib/rails/application.rb:304:in `initialize_console'
        from /usr/lib/ruby/gems/1.9.1/gems/railties-3.2.12/lib/rails/application.rb:152:in `load_console'
        from /usr/lib/ruby/gems/1.9.1/gems/railties-3.2.12/lib/rails/commands/console.rb:27:in `start'
        from /usr/lib/ruby/gems/1.9.1/gems/railties-3.2.12/lib/rails/commands/console.rb:8:in `start'
        from /usr/lib/ruby/gems/1.9.1/gems/railties-3.2.12/lib/rails/commands.rb:41:in `<top (required)>'
        from script/rails:6:in `require'
        from script/rails:6:in `<main>'

$ uname -a
CYGWIN_NT-5.1 dumbopc 1.7.17(0.262/5/3) 2012-10-19 14:39 i686 Cygwin