JRuby 1.0.1 fails to start if assertions are enabled. It looks like the assertion of line 109 of DynamicScope throws a NPE for variableValues. It may be best to enable assertions while the tests are run from the build file. >java -enableassertions -jar jruby-complete-1.0.1.jar --command irb DynamicScope.java:109:in `org.jruby.runtime.DynamicScope.setValue': java.lang.NullPointerException: null (NativeException) from AssignmentVisitor.java:186:in `org.jruby.evaluator.AssignmentVisitor.localAsgnNode' from AssignmentVisitor.java:88:in `org.jruby.evaluator.AssignmentVisitor.assign' from Block.java:283:in `org.jruby.runtime.Block.setupBlockArg' from Block.java:213:in `org.jruby.runtime.Block.yield' from Block.java:186:in `org.jruby.runtime.Block.yield' from RubyArray.java:1283:in `org.jruby.RubyArray.each' from null:-1:in `org.jruby.RubyArrayInvokereach0.call' from InvocationCallback.java:49:in `org.jruby.runtime.callback.InvocationCallback.execute' ... 72 levels... from file:/Users/regg002/.m2/repository/org/jruby/jruby-complete/1.0.1/jruby-complete-1.0.1.jar!/jruby/commands.rb:29:in `require' from file:/Users/regg002/.m2/repository/org/jruby/jruby-complete/1.0.1/jruby-complete-1.0.1.jar!/jruby/commands.rb:29:in `jirb' from :1 Complete Java stackTrace java.lang.NullPointerException at org.jruby.runtime.DynamicScope.setValue(DynamicScope.java:109) at org.jruby.evaluator.AssignmentVisitor.localAsgnNode(AssignmentVisitor.java:186) at org.jruby.evaluator.AssignmentVisitor.assign(AssignmentVisitor.java:88) at org.jruby.runtime.Block.setupBlockArg(Block.java:283) at org.jruby.runtime.Block.yield(Block.java:213) at org.jruby.runtime.Block.yield(Block.java:186) at org.jruby.RubyArray.each(RubyArray.java:1283)