在Karma / Jasmine getModifierState中测试

Question

如何测试此方法（角度）：

 public detectCapslock(event: KeyboardEvent): void {
        let capsOn: boolean = event.getModifierState && event.getModifierState("CapsLock");
        if (capsOn) {
            this.capsOn = "Caps Lock on";
        } else {
            this.capsOn = "";
        }
    }