Adds testing

[zgosalvez]

No description provided.

[bartosz347]

@zgosalvez On the subject of the upgrade of lcov-total to v2, there are at least 2 options:

1. Migrate whole project to ESM (I'm not sure if ESM is supported by GitHub Actions and ncc)
2. Use import like described here.

This quick PoC seems to work with Node directly (an isolated run of only a single function), but Jest is throwing an error.

async function foo() {
  const lcovTotal = await import('lcov-total/src/index.js');

  lcovTotal.default("foo-file");
}