FIX: Undo/redo delete/add page

Now we can undo adding or deleting worksheets

base/src/test/user_model/mod.rs

@@ -16,6 +16,7 @@ mod test_paste_csv;
 mod test_rename_sheet;
 mod test_row_column;
 mod test_sheet_state;
+mod test_sheets_undo_redo;
 mod test_styles;
 mod test_to_from_bytes;
 mod test_undo_redo;

base/src/test/user_model/test_add_delete_sheets.rs

@@ -25,9 +25,6 @@ fn add_undo_redo() {
     assert_eq!(model.get_formatted_cell_value(2, 1, 1), Ok("6".to_string()));
 
     model.delete_sheet(1).unwrap();
-
-    assert!(!model.can_undo());
-    assert!(!model.can_redo());
 }
 
 #[test]

base/src/test/user_model/test_sheets_undo_redo.rs

@@ -0,0 +1,52 @@
+#![allow(clippy::unwrap_used)]
+
+use crate::test::util::new_empty_model;
+use crate::UserModel;
+
+#[test]
+fn basic_undo_redo() {
+    let model = new_empty_model();
+    let mut model = UserModel::from_model(model);
+    assert_eq!(model.get_selected_sheet(), 0);
+
+    model.new_sheet().unwrap();
+    assert_eq!(model.get_selected_sheet(), 1);
+    model.undo().unwrap();
+    assert_eq!(model.get_selected_sheet(), 0);
+    {
+        let props = model.get_worksheets_properties();
+        assert_eq!(props.len(), 1);
+        let view = model.get_selected_view();
+        assert_eq!(view.sheet, 0);
+    }
+
+    model.redo().unwrap();
+    assert_eq!(model.get_selected_sheet(), 1);
+    {
+        let props = model.get_worksheets_properties();
+        assert_eq!(props.len(), 2);
+        let view = model.get_selected_view();
+
+        assert_eq!(view.sheet, 1);
+    }
+}
+
+#[test]
+fn delete_undo() {
+    let model = new_empty_model();
+    let mut model = UserModel::from_model(model);
+    assert_eq!(model.get_selected_sheet(), 0);
+
+    model.new_sheet().unwrap();
+    assert_eq!(model.get_selected_sheet(), 1);
+    model.set_user_input(1, 1, 1, "42").unwrap();
+    model.set_user_input(1, 1, 2, "=A1*2").unwrap();
+    model.delete_sheet(1).unwrap();
+
+    assert_eq!(model.get_selected_sheet(), 0);
+
+    model.undo().unwrap();
+    assert_eq!(model.get_selected_sheet(), 1);
+    model.redo().unwrap();
+    assert_eq!(model.get_selected_sheet(), 0);
+}