test: add coverage tests for run() with isolation: 'none'

Verify that:
  - run({ coverage: true, isolation: 'none' }) reports src files,
  - default test-file exclusion drops *.test.mjs in both isolation
    modes,
  - the path is idempotent when --experimental-test-coverage is set
    on the same process.

Refs: #60023
Signed-off-by: sangwook <rewq5991@gmail.com>

Author: Han5991

test/fixtures/test-runner/coverage-isolation-none/src/foo.mjs

@@ -0,0 +1,11 @@
+export function add(a, b) {
+  return a + b;
+}
+
+export function sub(a, b) {
+  return a - b;
+}
+
+export function unused() {
+  return 'unused';
+}

test/fixtures/test-runner/coverage-isolation-none/tests/foo.test.mjs

@@ -0,0 +1,11 @@
+import test from 'node:test';
+import assert from 'node:assert';
+import { add, sub } from '../src/foo.mjs';
+
+test('add', () => {
+  assert.strictEqual(add(2, 3), 5);
+});
+
+test('sub', () => {
+  assert.strictEqual(sub(5, 3), 2);
+});

test/parallel/test-runner-coverage-isolation-none-api.mjs

@@ -0,0 +1,92 @@
+import * as common from '../common/index.mjs';
+import { before, describe, it, run } from 'node:test';
+import assert from 'node:assert';
+import { spawnSync } from 'node:child_process';
+import { cp, writeFile } from 'node:fs/promises';
+import { join, sep } from 'node:path';
+import tmpdir from '../common/tmpdir.js';
+import fixtures from '../common/fixtures.js';
+
+const skipIfNoInspector = {
+  skip: !process.features.inspector ? 'inspector disabled' : false,
+};
+
+tmpdir.refresh();
+
+async function setupFixtures() {
+  const fixtureDir = fixtures.path('test-runner', 'coverage-isolation-none');
+  await cp(fixtureDir, tmpdir.path, { recursive: true });
+}
+
+describe('run() coverage with isolation: none', skipIfNoInspector, () => {
+  before(async () => {
+    await setupFixtures();
+  });
+
+  for (const isolation of ['none', 'process']) {
+    it(`reports src coverage and excludes test files by default (isolation=${isolation})`, async () => {
+      const stream = run({
+        files: [join(tmpdir.path, 'tests', 'foo.test.mjs')],
+        coverage: true,
+        isolation,
+        cwd: tmpdir.path,
+      });
+      stream.on('test:fail', common.mustNotCall());
+
+      let summary;
+      stream.on('test:coverage', common.mustCall(({ summary: s }) => {
+        summary = s;
+      }));
+      // eslint-disable-next-line no-unused-vars
+      for await (const _ of stream);
+
+      assert.ok(summary, 'test:coverage event must fire');
+      const paths = summary.files.map((f) => f.path);
+      assert.ok(
+        paths.length > 0,
+        `coverage files must be reported (isolation=${isolation}); got ${JSON.stringify(paths)}`,
+      );
+      assert.ok(
+        paths.some((p) => p.endsWith(`src${sep}foo.mjs`)),
+        `expected src/foo.mjs to be present (isolation=${isolation}); got ${JSON.stringify(paths)}`,
+      );
+      assert.ok(
+        paths.every((p) => !p.endsWith('foo.test.mjs')),
+        `expected foo.test.mjs to be excluded by default (isolation=${isolation}); got ${JSON.stringify(paths)}`,
+      );
+    });
+  }
+
+  it('is idempotent when --experimental-test-coverage is also passed', async () => {
+    const runnerPath = join(tmpdir.path, 'runner.mjs');
+    await writeFile(runnerPath, `\
+import { run } from 'node:test';
+import { join } from 'node:path';
+
+const stream = run({
+  files: [join(import.meta.dirname, 'tests', 'foo.test.mjs')],
+  coverage: true,
+  isolation: 'none',
+  cwd: import.meta.dirname,
+});
+stream.on('test:fail', () => process.exit(10));
+let summary;
+stream.on('test:coverage', (event) => { summary = event.summary; });
+for await (const _ of stream);
+if (!summary || summary.files.length === 0) process.exit(11);
+const hasSrc = summary.files.some((f) => f.path.endsWith('foo.mjs') && !f.path.endsWith('foo.test.mjs'));
+const hasTest = summary.files.some((f) => f.path.endsWith('foo.test.mjs'));
+if (!hasSrc) process.exit(12);
+if (hasTest) process.exit(13);
+`);
+    const result = spawnSync(process.execPath, [
+      '--experimental-test-coverage',
+      runnerPath,
+    ], { cwd: tmpdir.path });
+    assert.strictEqual(
+      result.status,
+      0,
+      `exited with ${result.status}\nstderr: ${result.stderr}\nstdout: ${result.stdout}`,
+    );
+  });
+});