Close but not quite right syntax...many ways you can do, but
test_means = cellfun(@(x) mean(x.Var1),test);
should do the trick presuming you maintained the same variable names for each table.
Use the proper variable name for your table, of course, not the default Var1 unless it is the right name, of course.
cellfun passes the content of the cell; in this case this is still a table so have to dereference it.