better framework for running arm test

more explicit, rather than gobbling files, pass code in
preload is available (so code does not have to be duplicated)
interpret first, so bad mistakes get caught
no ssh, just qemu-arm, configure through env

test/mains/test_assign.rb

@@ -0,0 +1,31 @@
+require_relative "helper"
+
+module Mains
+  class AssignTester < MiniTest::Test
+    include MainsHelper
+
+    def test_local
+      @input = as_main 'a = 15 ; return a'
+      assert_result  15 , ""
+    end
+
+    def test_plus
+      @preload = "Integer.plus"
+      @input = as_main("a = 5 + 5 ; return a")
+      assert_result 10 , ""
+    end
+
+    def test_plus2
+      @preload = "Integer.plus"
+      @input = as_main("a = 5 ;a = 5 + a ; return a")
+      assert_result 10 , ""
+    end
+
+    def test_plus3
+      @preload = "Integer.plus"
+      @input = as_main("a = 5 ;a = 5 + a ;a = a + 5; return a")
+      assert_result 15 , ""
+    end
+
+  end
+end