fix(grid): dynamic column-group children setup

Author: damyanpetev

projects/igniteui-angular/src/lib/grids/columns/column-group.component.ts

@@ -10,6 +10,7 @@ import {
     Output,
     EventEmitter
 } from '@angular/core';
+import { takeUntil } from 'rxjs/operators';
 
 import { IgxColumnComponent } from './column.component';
 import { flatten } from '../../core/utils';
@@ -298,6 +299,15 @@ export class IgxColumnGroupComponent extends IgxColumnComponent implements After
         if (this.collapsible) {
             this.setExpandCollapseState();
         }
+
+        this.children.changes
+            .pipe(takeUntil(this.destroy$))
+            .subscribe((change: QueryList<IgxColumnComponent>) => {
+                change.forEach(x => x.parent = this);
+                if (this.collapsible) {
+                    this.setExpandCollapseState();
+                }
+            });
     }
 
     /**

projects/igniteui-angular/src/lib/grids/grid/column-group.spec.ts

@@ -135,7 +135,7 @@ describe('IgxGrid - multi-column headers #grid', () => {
 
         }));
 
-        it('Should render dynamic column group header correctly (#12165).', fakeAsync(() => {
+        it('Should render dynamic column group header correctly (#12165).', () => {
             fixture = TestBed.createComponent(BlueWhaleGridComponent) as ComponentFixture<BlueWhaleGridComponent>;
             (fixture as ComponentFixture<BlueWhaleGridComponent>).componentInstance.firstGroupRepeats = 1;
             (fixture as ComponentFixture<BlueWhaleGridComponent>).componentInstance.secondGroupRepeats = 1;
@@ -172,7 +172,7 @@ describe('IgxGrid - multi-column headers #grid', () => {
             firstSixHeaders = allHeaders.slice(0, 6).map(x => x.column.field);
             expect(allHeaders.length).toEqual(15);
             expect(firstSixHeaders).toEqual(['ID', 'Missing', 'ID', 'ID', 'ID', 'CompanyName']);
-        }));
+        });
 
         it('Should not render empty column group.', () => {
             fixture = TestBed.createComponent(ColumnGroupTestComponent);