function subsetTest(testFunc, ...args) {
    currentSubTest++;
    if (shouldRunSubTest(currentSubTest)) {
      return testFunc(...args);
    }
    return null;
  }
Only test a subset of tests with, e.g., `?1-10` in the URL.
Can be used together with `<meta name="variant" content="...">`
Sample usage:
for (const test of tests) {
  subsetTest(async_test, test.fn, test.name);
}