test_runner: make end of work check stricter

lib/internal/test_runner/test.js

@@ -822,11 +822,20 @@ class Test extends AsyncResource {
         this.parent.activeSubtests--;
       }
 
+      // The call to processPendingSubtests() below can change the number of
+      // pending subtests. When detecting if we are done running tests, we want
+      // to check if there are no pending subtests both before and after
+      // calling processPendingSubtests(). Otherwise, it is possible to call
+      // root.run() multiple times (which is harmless but can trigger an
+      // EventEmitter leak warning).
+      const pendingSiblingCount = this.parent.pendingSubtests.length;
+
       this.parent.addReadySubtest(this);
       this.parent.processReadySubtestRange(false);
       this.parent.processPendingSubtests();
 
       if (this.parent === this.root &&
+          pendingSiblingCount === 0 &&
           this.root.activeSubtests === 0 &&
           this.root.pendingSubtests.length === 0 &&
           this.root.readySubtests.size === 0) {

test/parallel/test-runner-filter-warning.js

@@ -0,0 +1,11 @@
+// Flags: --test-only
+'use strict';
+const common = require('../common');
+const { test } = require('node:test');
+const { defaultMaxListeners } = require('node:events');
+
+process.on('warning', common.mustNotCall());
+
+for (let i = 0; i < defaultMaxListeners + 1; ++i) {
+  test(`test ${i + 1}`);
+}