reqrote return sequence with builder

added test _before_ , same code, just much easier to read
in preparation for returning messages

test/mom/instruction/test_return_sequence.rb

@@ -0,0 +1,41 @@
+require_relative "../helper"
+
+module Risc
+  class TestReturnSequence < MiniTest::Test
+    include Statements
+
+    def setup
+      super
+      @input = "5.div4"
+      @expect = "something"
+      @produced = produce_instructions
+    end
+    def main_ends
+      24
+    end
+    def test_postamble_classes
+      postamble.each_with_index do |ins , index|
+        assert_equal ins , @produced.next( main_ends + index).class
+      end
+    end
+    def test_main_label
+      assert_equal Label , @produced.next(main_ends).class
+      assert_equal "return_label" , @produced.next(main_ends).name
+    end
+    def test_move_ret
+      assert_slot_to_reg( @produced.next(main_ends + 1) , :r0 ,  5 ,  :r1 )
+    end
+    def test_move_caller
+      assert_slot_to_reg( @produced.next(main_ends + 2) , :r0 ,  6 ,  :r2 )
+    end
+    def test_save_ret
+      assert_reg_to_slot( @produced.next(main_ends + 3) , :r1  ,  :r2 ,  5 )
+    end
+    def test_save_addr
+      assert_slot_to_reg( @produced.next(main_ends + 4) , :r0 ,  4 ,  :r1 )
+    end
+    def test_reduce_addr
+      assert_slot_to_reg( @produced.next(main_ends + 5) , :r1 ,  2 ,  :r1 )
+    end
+  end
+end