add rewriting of operator assignment

foo += 1 becomes foo = foo + 1 in vool

test/vool/ruby_compiler/test_ivar_assignment.rb

@@ -1,7 +1,7 @@
 require_relative "helper"
 
 module Vool
-  class TestAssignment < MiniTest::Test
+  class TestIvarAssignment < MiniTest::Test
 
     def test_local
       lst = RubyCompiler.compile( "foo = bar")

test/vool/ruby_compiler/test_local_assignment.rb

@@ -1,7 +1,7 @@
 require_relative "helper"
 
 module Vool
-  class TestLocal < MiniTest::Test
+  class TestLocalAssignment < MiniTest::Test
 
     def test_local
       lst = RubyCompiler.compile( "foo = bar")

test/vool/ruby_compiler/test_op_assignment.rb

@@ -0,0 +1,39 @@
+require_relative "helper"
+
+module Vool
+  module OpAss
+    def test_local_name
+      assert_equal :foo , @lst.name
+    end
+    def test_local_value
+      assert_equal SendStatement , @lst.value.class
+    end
+    def test_local_method
+      assert_equal :+ , @lst.value.name
+    end
+    def test_local_receiver
+      assert_equal :foo , @lst.value.receiver.name
+    end
+    def test_local_receiver
+      assert_equal 5 , @lst.value.arguments.first.value
+    end
+  end
+  class TestLocalOpAssign < MiniTest::Test
+    include OpAss
+    def setup
+      @lst = RubyCompiler.compile( "foo += 5")
+    end
+    def test_local_ass
+      assert_equal LocalAssignment , @lst.class
+    end
+  end
+  class TestIvarOpAssign < MiniTest::Test
+    include OpAss
+    def setup
+      @lst = RubyCompiler.compile( "@foo += 5")
+    end
+    def test_ivar_ass
+      assert_equal IvarAssignment , @lst.class
+    end
+  end
+end