IMicrotasks

interface IMicrotasks {
  /** Queues a callback to run at the next microtask checkpoint. */
  queue(callback: () => void): void;
}

/** The `IMicrotasks` of a fixed/manual/sequential Time-Provider - see `timeProvider.scheduler.microtasks`. */
interface IDeterministicMicrotasks extends IMicrotasks {
  /** Runs every callback queued through `queue`, in order, until the queue is empty. */
  drain(): void;
}

timeProvider.scheduler.microtasks.queue is the host's own queueMicrotask on a system runtime, and the runtime's own queue on a fixed/manual/sequential one, drained around due callbacks and scheduling calls. timeProvider.scheduler.microtasks.drain (only on IDeterministicMicrotasks, i.e. for a fixed, manual, or sequential Time-Provider) runs that checkpoint on demand. See Microtasks for the full breakdown, including firing order and what disposal does to a still-queued microtask.

timeProvider.scheduler.microtasks.queue(() => log.push("m1"));