def with_backtrace(bt, &block)
      bt ||= []
      begin
        @__assert_with_bt__.push(bt.first)
        instance_eval(&block)
      rescue Result::TestSkipped, Result::TestFailure => e
        if e.assert_with_bt.nil? && !@__assert_with_bt__.empty?
          e.assert_with_bt = @__assert_with_bt__.dup
        end
        raise(e)
      ensure
        @__assert_with_bt__.pop
      end
    end
def with_backtrace(bt, &block)
      bt ||= []
      begin
        @__assert_with_bt__.push(bt.first)
        instance_eval(&block)
      rescue Result::TestSkipped, Result::TestFailure => e
        if e.assert_with_bt.nil? && !@__assert_with_bt__.empty?
          e.assert_with_bt = @__assert_with_bt__.dup
        end
        raise(e)
      ensure
        @__assert_with_bt__.pop
      end
    end
alter the backtraces of fail/skip results generated in the given block