Can not run any unit test for Redmine with Ruby 2.0.0 under Windows. Is that at all possible?

Any attempt to run unit tests for Redmine, like:

ruby test/unit/issue_custom_field_test.rb

produces this:

DL is deprecated, please use Fiddle

C:/Develop/Ruby200/lib/ruby/gems/2.0.0/gems/activesupport-4.2.4/lib/active_support/dependencies.rb:274:in `require': cannot load such file --
mocha/setup (LoadError)
        from C:/Develop/Ruby200/lib/ruby/gems/2.0.0/gems/activesupport-4.2.4/lib/active_support/dependencies.rb:274:in `block in require'
        from C:/Develop/Ruby200/lib/ruby/gems/2.0.0/gems/activesupport-4.2.4/lib/active_support/dependencies.rb:240:in `load_dependency'
        from C:/Develop/Ruby200/lib/ruby/gems/2.0.0/gems/activesupport-4.2.4/lib/active_support/dependencies.rb:274:in `require'
        from C:/Develop/Redmine/src/redmine/test/test_helper.rb:36:in `<top (required)>'
        from C:/Develop/Ruby200/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in `require'
        from C:/Develop/Ruby200/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in `require'
        from test/unit/issue_custom_field_test.rb:18:in `<main>'

I've googled everywhere I could. No luck so far.

Any ideas? Would be great.

PS: mocha is installed:

C:\Develop\Redmine\src\redmine>gem list | grep -B 2 -A 2 mocha

mini_portile (0.6.2)
minitest (5.8.3, 4.3.2)
mocha (1.1.0)
mysql2 (0.3.20 x86-mingw32)
net-ldap (0.12.1)