fix interpreter to use positions

tick from one (simulated memory) position to the next
(not from one instruction to the next)

test/risc/test_interpreter.rb

@@ -0,0 +1,54 @@
+require_relative "helper"
+
+module Risc
+  class TestInterpreterBasics < MiniTest::Test
+
+    def test_class
+      assert_equal Risc::Interpreter , Interpreter.new.class
+    end
+    def test_starts_stopped
+      assert_equal :stopped , Interpreter.new.state
+    end
+    def test_has_regs
+      assert_equal 12 , Interpreter.new.registers.length
+    end
+    def test_has_r0
+      assert_equal :r0 , Interpreter.new.registers.keys.first
+    end
+  end
+  class TestInterpreterStarts < MiniTest::Test
+    def setup
+      @machine = Risc.machine.boot
+      @machine.translate(:interpreter)
+      @machine.position_all
+      @interpreter = Interpreter.new
+    end
+    def test_starts
+      assert_equal 0 , @interpreter.start_machine
+    end
+    def test_started
+      @interpreter.start_machine
+      assert_equal :running , @interpreter.state
+    end
+    def test_pos
+      @interpreter.start_machine
+      assert_equal 0 , @interpreter.clock
+    end
+  end
+  class TestInterpreterTicks < MiniTest::Test
+    def setup
+      @machine = Risc.machine.boot
+      @machine.translate(:interpreter)
+      @machine.position_all
+      @interpreter = Interpreter.new
+      @interpreter.start_machine
+    end
+    def test_tick
+      assert_equal 19484 , @interpreter.tick
+    end
+    def test_tick
+      assert_equal 19484 , @interpreter.tick
+      assert_equal 19488 , @interpreter.tick
+    end
+  end
+end