A nasty pop2+keep bug

src/stack/pop.rs

@@ -66,7 +66,7 @@ impl Stack for PopStack {
         if self._idx < 2 {
             return Err(StackError::StackUnderflow);
         }
-        let val = self.get2(self._idx - 1)?;
+        let val = self.get2(self._idx - 2)?;
         self._idx -= 2;
         Ok(val)
     }
@@ -78,7 +78,7 @@ mod test_ps {
     use crate::stack::arrs::ArrayStack;
 
     #[test]
-    fn test_dummy_pop() {
+    fn test_dummy_pop1() {
         // Set up the underlying stack...
         let underlying: Rc<RefCell<dyn Stack>> =
             Rc::new(RefCell::new(ArrayStack::of1(&[0xFF, 0xFE])));
@@ -96,6 +96,25 @@ mod test_ps {
         assert_eq!(underlying.borrow_mut().pop1().unwrap(), 0xFF);
     }
 
+    #[test]
+    fn test_dummy_pop2() {
+        // Set up the underlying stack...
+        let underlying: Rc<RefCell<dyn Stack>> =
+            Rc::new(RefCell::new(ArrayStack::of1(&[0xFF, 0xFE])));
+
+        // Set up the wrapper, which assumes it has exclusive access to the underlying stack
+        let wrapper: Rc<RefCell<dyn Stack>> =
+            Rc::new(RefCell::new(PopStack::new(underlying.clone())));
+
+        // We should be able to pop an appropriate short
+        assert_eq!(wrapper.borrow_mut().pop2().unwrap(), 0xFFFE);
+        assert_eq!(wrapper.borrow_mut().idx(), 0);
+
+        // And the underlying stack should be unaffected
+        assert_eq!(underlying.borrow_mut().pop1().unwrap(), 0xFE);
+        assert_eq!(underlying.borrow_mut().pop1().unwrap(), 0xFF);
+    }
+
     #[test]
     fn test_pop_pushthrough() {
         // Set up the underlying stack...