attq/test/retries.test.ts

import { withRetry } from "../src/retries";

const FAST_RETRY_CONFIG: Parameters<typeof withRetry>[1] = {
  attempts: 6,
  // Always retry almost immediately, even when using real timers.
  backoffMs: () => 1,
};

test("successful function only executes once", async () => {
  const fn = jest.fn(async () => "success!");
  const result = await withRetry(fn, FAST_RETRY_CONFIG)();
  expect(result).toEqual("success!");
  expect(fn).toHaveBeenCalledTimes(1);
});

test("failing function rejects after correct number of attempts", async () => {
  const fn = jest.fn(async () => {
    throw "oops!";
  });
  await expect(withRetry(fn, FAST_RETRY_CONFIG)()).rejects.toEqual("oops!");
  expect(fn).toHaveBeenCalledTimes(FAST_RETRY_CONFIG.attempts);
});

test("parameters are passed through", async () => {
  const fn = async (str: string, n: number) => {
    let result = "";
    for (let i = 0; i < n; i += 1) {
      result += str;
    }
    return result;
  };
  const retriable = withRetry(fn, FAST_RETRY_CONFIG);

  // A bit of type system hackery to assert at build time that function
  // signatures match.
  /* eslint-disable @typescript-eslint/no-unused-vars */
  type Assert<_T extends true> = void;
  type _ = Assert<typeof retriable extends typeof fn ? true : false>;
  /* eslint-enable @typescript-eslint/no-unused-vars */

  await expect(retriable("hello;", 3)).resolves.toEqual("hello;hello;hello;");
});

test("retries back off with expected delays", async () => {
  // Don't enable the `advanceTimers` configuration or else risk skewing the
  // timing scheme used in this test.
  jest.useFakeTimers();

  let n = 0;
  const fn = jest.fn(async () => {
    if (n < 5) {
      n += 1;
      throw "oops!";
    } else {
      // Fake timers don't play nicely with the `expect().rejects` API, so
      // ensure that the last attempt succeeds.
      return "success!";
    }
  });

  const promise = withRetry(
    fn,
    {
      attempts: 6,
      backoffMs: (attempt) => 1000 * 2 ** attempt,
    },
  )();

  expect(fn).toHaveBeenCalledTimes(1);
  await jest.advanceTimersByTimeAsync(100);
  expect(fn).toHaveBeenCalledTimes(1);

  await jest.advanceTimersByTimeAsync(1000);
  expect(fn).toHaveBeenCalledTimes(2);
  await jest.advanceTimersByTimeAsync(100);
  expect(fn).toHaveBeenCalledTimes(2);

  await jest.advanceTimersByTimeAsync(2000);
  expect(fn).toHaveBeenCalledTimes(3);
  await jest.advanceTimersByTimeAsync(100);
  expect(fn).toHaveBeenCalledTimes(3);

  await jest.advanceTimersByTimeAsync(4000);
  expect(fn).toHaveBeenCalledTimes(4);
  await jest.advanceTimersByTimeAsync(100);
  expect(fn).toHaveBeenCalledTimes(4);

  await jest.advanceTimersByTimeAsync(8000);
  expect(fn).toHaveBeenCalledTimes(5);
  await jest.advanceTimersByTimeAsync(100);
  expect(fn).toHaveBeenCalledTimes(5);

  await jest.advanceTimersByTimeAsync(16000);
  expect(fn).toHaveBeenCalledTimes(6);

  await expect(promise).resolves.toEqual("success!")

  // Mock timers without auto-advance enabled are a pain to manage when merely
  // counting retries, so use real timers and a very short backoff duration in
  // other tests instead.
  jest.useRealTimers();
});