Destroyable Angular component

destroyable.component.spec.ts

import { Subject } from 'rxjs';
import { Destroyable } from './destroyable.component';

class TestableDestroyable extends Destroyable { }

describe('Destroyable', () => {
    it('should construct with observable', () => {
        const component = new TestableDestroyable();
        expect(component.destroyed$ instanceof Subject).toBeTruthy();
    });

    it('should emit destroyed observable OnDestroy', done => {
        const component = new TestableDestroyable();
        component.destroyed$.subscribe(() => done());
        component.ngOnDestroy();
    });

    it('should emit destroyed observable OnDestroy', () => {
        const component = new TestableDestroyable();
        component.destroyed$.subscribe(() => { });
        component.ngOnDestroy();
        expect(component.destroyed$.isStopped).toBeTruthy();
    });
});

destroyable.component.ts

import { OnDestroy } from '@angular/core';
import { Subject } from 'rxjs';

export abstract class Destroyable implements OnDestroy {
    destroyed$ = new Subject();

    ngOnDestroy(): void {
        this.destroyed$.next();
        this.destroyed$.complete();
    }
}