function testSeparateSet(mechanism, mechanismSeparate) {
  mechanism.set('first', 'one');
  assertNull(mechanismSeparate.get('first'));
  assertEquals(0, mechanismSeparate.getCount());
  const it = mechanismSeparate[Symbol.iterator]().next();
  assertTrue(it.done);
  assertEquals(it.value, undefined);
}
@param {!IterableMechanism} mechanism
@param {!IterableMechanism} mechanismSeparate