The test does not directly load from cars.mat, but loads from another file.
Paste this into your scratch pad to work to test 1:
N = 5
load(fullfile(matlabroot, 'toolbox/stats/statsdemos', 'carbig.mat'));
Model = strtrim(string(Model));
cars = table(Model, MPG, Horsepower, Weight, Acceleration);
save cars.mat cars