unittests: Add tests for tv_list_idx_of_item

src/nvim/eval/typval.c

@@ -774,7 +774,7 @@ long tv_list_idx_of_item(const list_T *const l, const listitem_T *const item)
     return -1;
   }
   long idx = 0;
-  listitem_T *li;
+  const listitem_T *li;
   for (li = l->lv_first; li != NULL && li != item; li = li->li_next) {
     idx++;
   }

test/unit/eval/typval_spec.lua

@@ -1324,5 +1324,21 @@ describe('typval.c', function()
         end)
       end)
     end)
+    describe('idx_of_item()', function()
+      it('works', function()
+        local l = list(1, 2, 3, 4, 5)
+        local l2 = list(42, empty_list)
+        local lis = list_items(l)
+        local lis2 = list_items(l2)
+
+        for i, li in ipairs(lis) do
+          eq(i - 1, lib.tv_list_idx_of_item(l, li))
+        end
+        eq(-1, lib.tv_list_idx_of_item(l, lis2[1]))
+        eq(-1, lib.tv_list_idx_of_item(l, nil))
+        eq(-1, lib.tv_list_idx_of_item(nil, nil))
+        eq(-1, lib.tv_list_idx_of_item(nil, lis[1]))
+      end)
+    end)
   end)
 end)