Fix dragging cells down

src/vs/workbench/contrib/notebook/browser/viewModel/notebookViewModel.ts

@@ -539,7 +539,10 @@ export class NotebookViewModel extends Disposable implements FoldingRegionDelega
 	}
 
 	moveCellToIdx(index: number, newIdx: number, synchronous: boolean, pushedToUndoStack: boolean = true): boolean {
-		// TODO roblou - works differently if index > or < newIdx, fix, write tests
+		if (index < newIdx) {
+			// newIdx will be one less after index has been removed
+			newIdx--;
+		}
 
 		const viewCell = this.viewCells[index] as CellViewModel;
 		if (!viewCell) {

src/vs/workbench/contrib/notebook/test/notebookViewModel.test.ts

@@ -57,6 +57,67 @@ suite('NotebookViewModel', () => {
 		);
 	});
 
+	test('move cells down', function () {
+		withTestNotebook(
+			instantiationService,
+			blukEditService,
+			undoRedoService,
+			[
+				[['//a'], 'javascript', CellKind.Code, [], { editable: true }],
+				[['//b'], 'javascript', CellKind.Code, [], { editable: true }],
+				[['//c'], 'javascript', CellKind.Code, [], { editable: true }],
+			],
+			(editor, viewModel) => {
+				viewModel.moveCellToIdx(0, 0, false);
+				// no-op
+				assert.equal(viewModel.viewCells[0].getText(), '//a');
+				assert.equal(viewModel.viewCells[1].getText(), '//b');
+
+				viewModel.moveCellToIdx(0, 1, false);
+				// no-op (move to after this cell?)
+				assert.equal(viewModel.viewCells[0].getText(), '//a');
+				assert.equal(viewModel.viewCells[1].getText(), '//b');
+
+				viewModel.moveCellToIdx(0, 2, false);
+				// b, a, c
+				assert.equal(viewModel.viewCells[0].getText(), '//b');
+				assert.equal(viewModel.viewCells[1].getText(), '//a');
+				assert.equal(viewModel.viewCells[2].getText(), '//c');
+
+				viewModel.moveCellToIdx(0, 3, false);
+				// a, c, b
+				assert.equal(viewModel.viewCells[0].getText(), '//a');
+				assert.equal(viewModel.viewCells[1].getText(), '//c');
+				assert.equal(viewModel.viewCells[2].getText(), '//b');
+			}
+		);
+	});
+
+	test('move cells up', function () {
+		withTestNotebook(
+			instantiationService,
+			blukEditService,
+			undoRedoService,
+			[
+				[['//a'], 'javascript', CellKind.Code, [], { editable: true }],
+				[['//b'], 'javascript', CellKind.Code, [], { editable: true }],
+				[['//c'], 'javascript', CellKind.Code, [], { editable: true }],
+			],
+			(editor, viewModel) => {
+				viewModel.moveCellToIdx(1, 0, false);
+				// b, a, c
+				assert.equal(viewModel.viewCells[0].getText(), '//b');
+				assert.equal(viewModel.viewCells[1].getText(), '//a');
+
+				viewModel.moveCellToIdx(2, 0, false);
+				// c, b, a
+				assert.equal(viewModel.viewCells[0].getText(), '//c');
+				assert.equal(viewModel.viewCells[1].getText(), '//b');
+				assert.equal(viewModel.viewCells[2].getText(), '//a');
+			}
+		);
+	});
+
 	test('index', function () {
 		withTestNotebook(
 			instantiationService,