Google - Can My employer test me on My technical skills at any given time ? Is this legal ?

they can usely if in question or they are being rude they can basically do anything they want when it comes with their employees its not fair but they have different reasons why they need to test your skills this could be if a person does something that warrents the idea to do that causes a incident or a accident to workers or production issues if your performance is a issue what that means if your performance has changed any they could pull that on you but they wouldn't tell you that unless you signed something