Return deselected items

When setting items where the new iterable is missing previously selected items, return them in `getChangedDeselection`.

src/operations.js

@@ -1,6 +1,7 @@
 import {
   clone,
   curry,
+  difference,
   flow,
   includes,
   intersection,
@@ -27,7 +28,7 @@ const setItems = curry((itemsIterable, state) => {
     selected: intersection(state.selected, items),
     changed: {
       selected: [],
-      deselected: [],
+      deselected: difference(state.selected, items),
     },
     anchor: includes(state.anchor, items) ? state.anchor : null,
   }

test/set-items.ut.js

@@ -1,5 +1,6 @@
 import { flow } from 'lodash/fp'
 import {
+  getChangedDeselection,
   getSelection,
   init,
   rangeTo,
@@ -24,6 +25,17 @@ describe('setItems - updating the list of selectable items', () => {
       expectExactlySameMembers(getSelection(newState), ['C'])
     })
 
+    it('should return previously selected items as newly deselected', () => {
+      const state = init()
+
+      const newState = flow(
+        setItems(iterable(['A', 'B'])),
+        setSelection(['B']),
+        setItems(iterable(['A']))
+      )(state)
+
+      expectExactlySameMembers(getChangedDeselection(newState), ['B'])
+    })
   })
 
   it('should remove item from anchor that doesn\'t exist anymore', () => {