The present disclosure provides a method for testing an apparatus which comprises a set of operational subunits each comprising a moving element, wherein the moving elements move between respective first and second extreme positions, the method comprising: transferring to the apparatus stabilization control commands; transferring to the apparatus first latching-commands for latching to the first extreme position a candidate moving element which is a moving element of a candidate operational subunit; when the first latching control commands are in effect, measuring a first output frequency of an oscillator whose output is coupled to the candidate operational subunit in an electrical coupling setup which causes the output frequency of the oscillator to depend on positions of a plurality of moving elements which comprises the candidate moving element; and based on the first output frequency determining a state of the candidate operational subunit.