中文
devexamples

Deterministic Retry Test Harness

A test harness that drives retry logic with scripted outcomes and a fake clock, so retry behaviour is verified without real delays.

TypescriptCli Tooling

Code

export type Outcome<T> = { readonly ok: true; readonly value: T } | { readonly ok: false; readonly error: Error };

export function ok<T>(value: T): Outcome<T> {
  return { ok: true, value };
}

export function fail(message: string): Outcome<never> {
  return { ok: false, error: new Error(message) };
}

export interface AttemptLog {
  readonly index: number;
  readonly at: number;
  readonly result: "ok" | "error";
}

export interface RetryHarness<T> {
  readonly attempts: AttemptLog[];
  readonly loader: () => Promise<T>;
  readonly exhausted: () => boolean;
}

export function createHarness<T>(
  script: readonly Outcome<T>[],
  clock: { now: () => number; setTimeout: (fn: () => void, ms: number) => unknown },
): RetryHarness<T> {
  const attempts: AttemptLog[] = [];
  let index = 0;

  const loader = async (): Promise<T> =>
    new Promise<T>((resolve, reject) => {
      const outcome = script[index];
      attempts.push({
        index,
        at: clock.now(),
        result: outcome.ok ? "ok" : "error",
      });
      index += 1;
      if (outcome.ok) resolve(outcome.value);
      else reject(outcome.error);
    });

  return {
    attempts,
    loader,
    exhausted: () => index >= script.length,
  };
}

Related Examples