test: make test fails when jest force-stops a worker (closes #711)

When a test leaves a timer running, jest force-stops that worker, prints
a warning, and the run still passes. Jest has no option that fails the
run instead. Both test scripts in package.json now run jest through
script/lib/jest.js. It passes jest's output through and exits 1 when
jest printed that warning.

Model: opus-5-5

eslint.config.js

@@ -153,7 +153,8 @@ module.exports = [
         },
     },
 
-    // The files in script/lib/ run on plain node too, and are never bundled.
+    // The helpers the script/ entrypoints call: plain node programs too, run
+    // from a shell script rather than from yarn, and never bundled.
     {
         files: ["script/lib/**/*.js"],
         languageOptions: {

script/lib/jest.js

@@ -1,40 +1,33 @@
 // Runs jest with the arguments it is given, and fails the run when jest had to
-// force-stop the worker process that ran a test file. Jest itself only prints a
-// warning when that happens, and its run still passes. The warning means a test
-// left a timer or another open handle running. The test scripts in package.json
-// run jest through this file.
-//
-// Jest runs inside this process and writes to the terminal directly, so its
-// output looks the same as a plain jest run. This file only checks each write
-// to stderr for the warning below.
+// force-stop a worker. Jest itself only prints a warning when that happens, and
+// its run still passes. The warning means a test left a timer or another open
+// handle running. The test scripts in package.json run jest through this file.
 
 "use strict";
 
+const { spawn } = require("child_process");
+
 // The start of the warning that jest prints on stderr after it force-stops a
-// worker process.
+// worker.
 const WORKER_WARNING = "A worker process has failed to exit gracefully";
 
-let forceStopped = false;
-
-const writeStderr = process.stderr.write.bind(process.stderr);
-process.stderr.write = (chunk, ...rest) => {
-    if (String(chunk).includes(WORKER_WARNING)) {
-        forceStopped = true;
-    }
-    return writeStderr(chunk, ...rest);
-};
-
-// Runs after jest has finished, as the process exits.
-process.on("exit", () => {
-    if (forceStopped) {
-        console.error(
-            "script/lib/jest.js: failing the run, because jest force-stopped " +
-                "a worker process. A test left a timer or another open " +
-                "handle running.",
-        );
-        process.exitCode = 1;
-    }
+const jest = spawn("jest", process.argv.slice(2), {
+    stdio: ["inherit", "inherit", "pipe"],
 });
 
-// Jest's own command-line program. It reads its arguments from process.argv.
-require("jest/bin/jest");
+let stderr = "";
+jest.stderr.on("data", (chunk) => {
+    process.stderr.write(chunk);
+    stderr += chunk;
+});
+
+jest.on("close", (code) => {
+    if (stderr.includes(WORKER_WARNING)) {
+        console.error(
+            "script/lib/jest.js: failing the run, because jest force-stopped " +
+                "a worker. A test left a timer or another open handle running.",
+        );
+        process.exit(1);
+    }
+    process.exit(code ?? 1);
+});