test_runner: fix recursive run

lib/internal/test_runner/runner.js

@@ -519,6 +519,8 @@ function run(options = kEmptyObject) {
   root.harness.shouldColorizeTestFiles ||= shouldColorizeTestFiles(root);
 
   if (process.env.NODE_TEST_CONTEXT !== undefined) {
+    process.emitWarning('node:test run() is being called recursively within a test file. skipping running files.');
+    root.postRun();
     return root.reporter;
   }
   let testFiles = files ?? createTestFileList();

test/fixtures/test-runner/recursive_run.js

@@ -0,0 +1,7 @@
+'use strict';
+
+const { test, run } = require('node:test');
+
+test('recursive run() calls', async () => {
+  for await (const event of run({ files: [__filename] }));
+});

test/parallel/test-runner-run.mjs

@@ -522,6 +522,18 @@ describe('require(\'node:test\').run', { concurrency: true }, () => {
     // eslint-disable-next-line no-unused-vars
     for await (const _ of stream);
   });
+
+  it('should avoid running recursively', async () => {
+    const stream = run({ files: [join(testFixtures, 'recursive_run.js')] });
+    let stderr = '';
+    stream.on('test:fail', common.mustNotCall());
+    stream.on('test:pass', common.mustCall(1));
+    stream.on('test:stderr', (c) => { stderr += c.message; });
+
+    // eslint-disable-next-line no-unused-vars
+    for await (const _ of stream);
+    assert.match(stderr, /Warning: run\(\) is being called recursively/);
+  });
 });
 
 describe('forceExit', () => {