lemon 0.9.0 fails tests

[graaff]

Trying to run lemon 0.9.0's test suite with 'rake test' I get the following error in ruby-test:

/usr/lib64/ruby/gems/1.8/gems/test-0.2.1/lib/test/rake.rb:85:in `run': undefined method `new' for #<Test::Rake::TestTask:0x7f4624826fb0> (NoMethodError)
    from /usr/lib64/ruby/gems/1.8/gems/test-0.2.1/lib/test/rake.rb:76:in `fork'
    from /usr/lib64/ruby/gems/1.8/gems/test-0.2.1/lib/test/rake.rb:76:in `run'
    from /usr/lib64/ruby/gems/1.8/gems/test-0.2.1/lib/test/rake.rb:70:in `define_task'
    from /usr/lib64/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:636:in `call'
    from /usr/lib64/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:636:in `execute'
    from /usr/lib64/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:631:in `each'
    from /usr/lib64/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:631:in `execute'
    from /usr/lib64/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:597:in `invoke_with_call_chain'
    from /usr/lib64/ruby/1.8/monitor.rb:242:in `synchronize'
    from /usr/lib64/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:590:in `invoke_with_call_chain'
    from /usr/lib64/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:583:in `invoke'
    from /usr/lib64/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2051:in `invoke_task'
    from /usr/lib64/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2029:in `top_level'
    from /usr/lib64/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2029:in `each'
    from /usr/lib64/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2029:in `top_level'
    from /usr/lib64/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling'
    from /usr/lib64/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2023:in `top_level'
    from /usr/lib64/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2001:in `run'
    from /usr/lib64/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling'
    from /usr/lib64/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:1998:in `run'
    from /usr/lib64/ruby/gems/1.8/gems/rake-0.8.7/bin/rake:31
    from /usr/bin/rake:8:in `load'
    from /usr/bin/rake:8