test_runner: detect only tests when isolation is off

This commit updates the way the test runner processes 'only'
tests when process-based test isolation is disabled. The
--test-only flag is no longer necessary in this scenario. The
test runner will automatically detect 'only' tests and apply the
appropriate filtering.

Author: cjihrig

doc/api/cli.md

@@ -2336,7 +2336,7 @@ changes:
 -->
 
 Configures the test runner to only execute top level tests that have the `only`
-option set.
+option set. This flag is not necessary when test isolation is disabled.
 
 ### `--test-reporter`
 

doc/api/test.md

@@ -229,10 +229,10 @@ const { describe, it } = require('node:test');
 
 ## `only` tests
 
-If Node.js is started with the [`--test-only`][] command-line option, it is
-possible to skip all tests except for a selected subset by passing
-the `only` option to the tests that should run. When a test with the `only`
-option is set, all subtests are also run.
+If Node.js is started with the [`--test-only`][] command-line option or test
+isolation is disabled, it is possible to skip all tests except for a selected
+subset by passing the `only` option to the tests that should run. When a test
+with the `only` option is set, all subtests are also run.
 If a suite has the `only` option set, all tests within the suite are run,
 unless it has descendants with the `only` option set, in which case only those
 tests are run.

lib/internal/test_runner/harness.js

@@ -38,7 +38,8 @@ function createTestTree(rootTestOptions, globalOptions) {
   const buildPhaseDeferred = createDeferredPromise();
   const isFilteringByName = globalOptions.testNamePatterns ||
                             globalOptions.testSkipPatterns;
-  const isFilteringByOnly = globalOptions.only;
+  const isFilteringByOnly = globalOptions.only || (globalOptions.isTestRunner &&
+                                                   globalOptions.isolation === 'none');
   const harness = {
     __proto__: null,
     buildPromise: buildPhaseDeferred.promise,

test/parallel/test-runner-no-isolation-filtering.js

@@ -45,10 +45,8 @@ test('works with --test-name-pattern', () => {
 
   assert.strictEqual(child.status, 0);
   assert.strictEqual(child.signal, null);
-  assert.match(stdout, /# tests 1/);
+  assert.match(stdout, /# tests 0/);
   assert.match(stdout, /# suites 0/);
-  assert.match(stdout, /# pass 1/);
-  assert.match(stdout, /ok 1 - test one/);
 });
 
 test('works with --test-skip-pattern', () => {