clock.next() / await clock.nextAsync()

Advances the clock to the the moment of the first scheduled timer, firing it.

The nextAsync() will also break the event loop, allowing any scheduled promise callbacks to execute before running the timers.

import t from "tap";
import sinon from "sinon";

t.test("clock.next advances to the next scheduled timer", (t) => {
  const clock = sinon.useFakeTimers();

  let firstCalled = false;
  let secondCalled = false;

  setTimeout(() => {
    firstCalled = true;
  }, 10);

  setTimeout(() => {
    secondCalled = true;
  }, 20);

  // Advance to first timer
  clock.next();

  t.ok(firstCalled, "first callback should have fired");
  t.notOk(secondCalled, "second callback should not have fired yet");

  // Advance to second timer
  clock.next();

  t.ok(secondCalled, "second callback should have fired");

  clock.restore();
  t.end();
});

t.test("clock.nextAsync with promises", async (t) => {
  const clock = sinon.useFakeTimers();

  let called = false;

  setTimeout(() => {
    called = true;
  }, 10);

  // nextAsync breaks the event loop first
  await clock.nextAsync();

  t.ok(called, "callback should have fired");

  clock.restore();
  t.end();
});