The only time I have seen inspections to determine if chains are in your possession are big rig truckers. In this case, Caltrans is doing the inspections, not CHP.I have heard CHP making the vehicles turn around if they don't carry chains on I-5. Just ordered Z143 from Amazon for $74 a few dollars more than Walmart but I can't find any cheaper chain to buy locally.
From a practical standpoint, CHP does not have the staffing to stop every vehicle on a major highway to see if chains are buried in the trunk somewhere.
From a common sense standpoint, such a check point would create a traffic jamb 50 miles long.
This does mean inspections might (but very unlikely) occur on sparsely traveled secondary roads in the Sierra.
CHP and Caltrans will turn you around at a chain control checkpoint if chains are not mounted on a vehicle that should have them on.