test_runner: introduce NODE_TEST_WORKER_ID for improved concurrent te…

…st execution

Added a new environment variable, `NODE_TEST_WORKER_ID`, which ranges from 1 to N when `--experimental-test-isolation=process` is enabled and defaults to 1 when `--experimental-test-isolation=none` is used.

lib/internal/test_runner/runner.js

@@ -358,14 +358,14 @@ class FileTest extends Test {
   }
 }
 
-function runTestFile(path, filesWatcher, opts) {
+function runTestFile(path, filesWatcher, opts, workerId = 1) {
   const watchMode = filesWatcher != null;
   const testPath = path === kIsolatedProcessName ? '' : path;
   const testOpts = { __proto__: null, signal: opts.signal };
   const subtest = opts.root.createSubtest(FileTest, testPath, testOpts, async (t) => {
     const args = getRunArgs(path, opts);
     const stdio = ['pipe', 'pipe', 'pipe'];
-    const env = { __proto__: null, ...process.env, NODE_TEST_CONTEXT: 'child-v8' };
+    const env = { __proto__: null, ...process.env, NODE_TEST_CONTEXT: 'child-v8', NODE_TEST_WORKER_ID: workerId };
     if (watchMode) {
       stdio.push('ipc');
       env.WATCH_REPORT_DEPENDENCIES = '1';
@@ -724,8 +724,10 @@ function run(options = kEmptyObject) {
     runFiles = () => {
       root.harness.bootstrapPromise = null;
       root.harness.buildPromise = null;
+      let workerId = 1;
       return SafePromiseAllSettledReturnVoid(testFiles, (path) => {
-        const subtest = runTestFile(path, filesWatcher, opts);
+        const subtest = runTestFile(path, filesWatcher, opts, workerId);
+        workerId++;
         filesWatcher?.runningSubtests.set(path, subtest);
         return subtest;
       });
@@ -766,6 +768,7 @@ function run(options = kEmptyObject) {
 
             root.entryFile = resolve(testFile);
             debug('loading test file:', fileURL.href);
+            process.env.NODE_TEST_WORKER_ID = 1;
             try {
               await cascadedLoader.import(fileURL, parent, { __proto__: null });
             } catch (err) {