Test IF in Subscribe Karma and Jasmine

How to be inside a subscribe in Karma angular 6 ?

  this.watcher = this.media.subscribe((change: MediaChange) => {
            this.activeMediaQuery = change ? `'${change.mqAlias}' = (${change.mediaQuery})` : '';
            this.changeMqAlias = change.mqAlias;
            if (this.changeMqAlias == 'xs' || this.changeMqAlias == 'sm' || this.changeMqAlias == 'xl') {

                
                if (this.id) {
                   this.get(this.id);
                }
            }
        });