vitest >=5.0.0 added `--repeats`. It repeats every test regardless of the result, which is useful for hunting flaky tests. Older versions don't have it.

const fs = require("fs");
const path = require("path");
const cp = require("child_process");
const dir = "/w/repeats";
fs.rmSync(dir, { recursive: true, force: true });
fs.mkdirSync(dir, { recursive: true });
function write(file, text) {
  const p = path.join(dir, file);
  fs.mkdirSync(path.dirname(p), { recursive: true });
  fs.writeFileSync(p, text);
}
function vitest(args, cwd) {
  const r = cp.spawnSync(process.execPath, ["/w/node_modules/vitest/vitest.mjs", ...args], {
    cwd: cwd || dir,
    encoding: "utf8",
    env: { ...process.env, NO_COLOR: "1", CI: "1" },
    timeout: 40000,
  });
  return { status: r.status, out: (r.stdout || "") + (r.stderr || "") + (r.error ? String(r.error) : "") };
}

write("count.test.mjs", [
  "import { test } from 'vitest'",
  "import { appendFileSync } from 'node:fs'",
  "test('counted', () => { appendFileSync(new URL('./runs.txt', import.meta.url), 'x') })",
].join("\n") + "\n");
const r = vitest(["run", "--repeats", "2"]);
console.log(r.out);
const runsFile = path.join(dir, "runs.txt");
const runs = fs.existsSync(runsFile) ? fs.readFileSync(runsFile, "utf8").length : 0;
if (runs === 3 && r.status === 0) {
  console.log("PASS: --repeats 2 ran the test 3 times");
  process.exit(0);
}
// The symptoms of the old version: the CLI rejects --repeats, or the test runs only once.
const rejected = r.status !== 0 && runs === 0 && r.out.includes("Unknown option `--repeats`");
const once = r.status === 0 && runs === 1;
if (rejected || once) {
  console.error("FAIL: --repeats 2 did not run the test 3 times (" + (rejected ? "unknown option" : "ran once") + ")");
  process.exit(1);
}
console.error("ERROR: unexpected result (ran " + runs + " times, exit " + r.status + ")");
process.exit(2);

const fs = require("fs");
const path = require("path");
const cp = require("child_process");
const dir = "/w/repeats";
fs.rmSync(dir, { recursive: true, force: true });
fs.mkdirSync(dir, { recursive: true });
function write(file, text) {
  const p = path.join(dir, file);
  fs.mkdirSync(path.dirname(p), { recursive: true });
  fs.writeFileSync(p, text);
}
function vitest(args, cwd) {
  const r = cp.spawnSync(process.execPath, ["/w/node_modules/vitest/vitest.mjs", ...args], {
    cwd: cwd || dir,
    encoding: "utf8",
    env: { ...process.env, NO_COLOR: "1", CI: "1" },
    timeout: 40000,
  });
  return { status: r.status, out: (r.stdout || "") + (r.stderr || "") + (r.error ? String(r.error) : "") };
}

write("count.test.mjs", [
  "import { test } from 'vitest'",
  "import { appendFileSync } from 'node:fs'",
  "test('counted', () => { appendFileSync(new URL('./runs.txt', import.meta.url), 'x') })",
].join("\n") + "\n");
const r = vitest(["run", "--repeats", "2"]);
console.log(r.out);
const runsFile = path.join(dir, "runs.txt");
const runs = fs.existsSync(runsFile) ? fs.readFileSync(runsFile, "utf8").length : 0;
if (runs === 3 && r.status === 0) {
  console.log("PASS: --repeats 2 ran the test 3 times");
  process.exit(0);
}
// The symptoms of the old version: the CLI rejects --repeats, or the test runs only once.
const rejected = r.status !== 0 && runs === 0 && r.out.includes("Unknown option `--repeats`");
const once = r.status === 0 && runs === 1;
if (rejected || once) {
  console.error("FAIL: --repeats 2 did not run the test 3 times (" + (rejected ? "unknown option" : "ran once") + ")");
  process.exit(1);
}
console.error("ERROR: unexpected result (ran " + runs + " times, exit " + r.status + ")");
process.exit(2);