function testDbObserversFired() {
  var resolver = goog.Promise.withResolver();

  var query = db.select().from(j);
  db.observe(query, function(changes) {
    assertEquals(sampleJobs.length, changes.length);
    changes.forEach(function(changeEvent) {
      assertEquals(1, changeEvent.addedCount);
    });
    resolver.resolve();
  });

  simulateInsertionModification(j, sampleJobs);
  return resolver.promise;
}
Tests that Lovefield's observers are firing as a result of an external
backstore change.
@return {!IThenable}