We can still keep the existing tests around as a sort of "extra" test, but before we remove them, we should add tap tests to cover the additional cases.
It looks like npm test already only runs tests in test/tap.
npm run test-all runs a different set of tests that aren't encompassed by npm test. It's probably going to take a while to get the coverage in npm (and the other modules it uses) increased to the point where the TAP tests alone are authoritative.
npm run test-all