Why don't ALL voting machines get fed a test batch of ballots before the election to prevent tampering/hacking?

Question

... run a test batch of ballots through it (voting machine)

(Source: step 6.2 of Wisconsin's official vote recount manual, courtesy of Bobson's answer here).

As a software developer, this seems like an obvious (and extremely effective) step to ensure that a voting machine has not been tampered with / hacked. If you feed a test batch of ballots, with known count of expected results, you will know for sure if the machine is deviating in how it counts.

Obviously, a hack could theoretically be sophisticated enough to circumvent that (e.g. by only starting tampering at a certain time of after a certain "deductible" # of initial ballots are counted), but that still seems like a significant upgrade to anti-hacking/tampering capability compared to doing nothing at all.

As such,

Why don't ALL voting machines get fed a test batch of ballots before the election to prevent tampering/hacking? (as a required procedure before polls open).

this works even on machines where there are no paper ballots, because the inputs can be designed beforehand so you know the expected count without the need to check paper trail.

Answer 1

This seems relatively easy to defeat.

if (ELECTION_DAY == date) {
    make_my_candidate_win();
    restore_executable_from_backup();
} else {
    count_results_correctly();
}

That said, that they run test ballots during a recount does not prove or even suggest that they don't do it before the actual election. If anything, it suggests that they do do it before the actual election, as they are clearly aware of it.

The greater problem is that without a paper trail, they can't detect what actually happened. If the count is altered and the altering code is then replaced, there is no way to detect that the count was altered. Even if the altering code is still there, unless you can work backwards from the given count to the real count, the count is spoiled. But working backwards is not always possible. E.g.

if (MY_CANDIDATE == selection || my_candidate_count <= other_candidate_count) {
    my_candidate_count++;
} else {
    other_candidate_count++;
}

Since that uses the current vote balance to determine whether or not to mess up the vote, you can't even tell if the code altered the count. If the first vote is for the right candidate and that candidate leads from then on, this code has no effect on the results.

This is a solvable problem. For example:

1. Print ballot based on choices.
2. Voter takes ballot and inserts in optical reader.
3. Voter confirms that optical reader is showing votes as desired by voter.
4. If not, destroy ballot and start over.
5. If confirmed, drop ballot in box.

That can be reviewed and recounted by hand even. But it gives the advantages of computer control in making a valid selection and counting consistently.