I get some strange responses on Windows. I'll test on Linux shortly. c:\Program Files\Microsoft Visual Studio 8\VC>fri -f plain assert ------------------------------------------------------ Breakpoint#assert assert(context = nil, &condition) {|| ...} ------------------------------------------------------------------------ This asserts that the block evaluates to true. If it doesn't evaluate to true a breakpoint will automatically be created at that execution point. You can disable assert checking in production code by setting Breakpoint.optimize_asserts to true. (It will still be enabled when Ruby is run via the -d argument.) Example: person_name = "Foobar" assert { not person_name.nil? } Note: If you want to use this method from an unit test, you will have to call it by its full name, Breakpoint.assert. c:\Program Files\Microsoft Visual Studio 8\VC>fri -f plain assert_not_same nil c:\Program Files\Microsoft Visual Studio 8\VC>fri -f plain Test::Unit (druby://127.0.0.1:1310) c:/ruby/lib/ruby/1.8/rdoc/ri/ri_descriptions.rb:99:in ` concat': can't convert nil into Array (TypeError) from (druby://127.0.0.1:1310) c:/ruby/lib/ruby/1.8/rdoc/ri/ri_descriptio ns.rb:99:in `merge_in' from (druby://127.0.0.1:1310) c:/ruby/lib/ruby/gems/1.8/gems/fastri-0.1. 0.1/lib/fastri/ri_index.rb:323:in `get_class' from (druby://127.0.0.1:1310) c:/ruby/lib/ruby/gems/1.8/gems/fastri-0.1. 0.1/lib/fastri/ri_index.rb:319:in `get_class' from (druby://127.0.0.1:1310) c:/ruby/lib/ruby/gems/1.8/gems/fastri-0.1. 0.1/lib/fastri/ri_service.rb:174:in `info' from (druby://127.0.0.1:1310) c:/ruby/lib/ruby/gems/1.8/gems/fastri-0.1. 0.1/lib/fastri/ri_service.rb:259:in `capture_stdout' from (druby://127.0.0.1:1310) c:/ruby/lib/ruby/gems/1.8/gems/fastri-0.1. 0.1/lib/fastri/ri_service.rb:173:in `info' from (druby://127.0.0.1:1310) c:/ruby/lib/ruby/1.8/drb/drb.rb:1552:in `p erform_without_block' from (druby://127.0.0.1:1310) c:/ruby/lib/ruby/1.8/drb/drb.rb:1512:in `p erform' ... 7 levels... from (druby://127.0.0.1:1310) c:/ruby/lib/ruby/gems/1.8/gems/fastri-0.1. 0.1/bin/fastri-server:113 from (druby://127.0.0.1:1310) c:/ruby/bin/fastri-server:18 from c:/ruby/lib/ruby/gems/1.8/gems/fastri-0.1.0.1/bin/fri:66 from c:/ruby/bin/fri:18