chore: increase code coverage for new code

Author: ghiscoding

packages/common/src/core/__tests__/slickGrid.spec.ts

@@ -2139,6 +2139,19 @@ describe('SlickGrid core file', () => {
       expect(headerElm).toBeInstanceOf(HTMLDivElement);
       expect(headerElm.dataset.id).toBe('b');
     });
+
+    it('should return undefined from getHeaderColumn fallback when target column is hidden', () => {
+      const columns = [
+        { id: 'a', field: 'a', name: 'A', hidden: true },
+        { id: 'b', field: 'b', name: 'B' },
+      ] as Column[];
+      const rows = [{ id: 0, a: 'x', b: 'y' }];
+
+      grid = new SlickGrid<any, Column>(container, rows, columns, defaultOptions);
+      grid.init();
+
+      expect(grid.getHeaderColumn(0)).toBeUndefined();
+    });
   });
 
   describe('flashCell() method', () => {