[ruby/irb] Add a workaround to make IRB work with debug's tests

(ruby/irb#919)

ruby/irb@eb442c4dda

lib/irb.rb

@@ -1035,6 +1035,12 @@ def eval_input
               @context.evaluate(statement.code, line_no)
             when Statement::Command
               ret = statement.command_class.execute(@context, statement.arg)
+              # TODO: Remove this output once we have a better way to handle it
+              # This is to notify `debug`'s test framework that the current input has been processed
+              # We also need to have a way to restart/stop threads around command execution
+              # when being used as `debug`'s console.
+              # https://github.com/ruby/debug/blob/master/lib/debug/irb_integration.rb#L8-L13
+              puts "INTERNAL_INFO: {}" if @context.with_debugger && ENV['RUBY_DEBUG_TEST_UI'] == 'terminal'
               @context.set_last_value(ret)
             end