fix(test): resolve the macOS temp root through its symlink in the launcher and preview tests (#501)

Supersedes #301 by @VassagoDevteam, ported onto the current component layout with fixes from review.

Verified before merge: format, package boundaries, unit suite, build, and the browser tracking suite; a browser harness for the change where one applies; adversarial review applied.

Co-authored-by: Vassago DevTeam <[email protected]>

src/tooling/fixtureRoot.mjs

@@ -0,0 +1,21 @@
+import { mkdtemp, realpath } from 'node:fs/promises';
+import { tmpdir } from 'node:os';
+import path from 'node:path';
+
+/**
+ * Create a temporary directory for a test fixture, resolved to its physical
+ * path.
+ *
+ * The system temp directory is reached through a symlink on macOS
+ * (`/var` -> `/private/var`, `/tmp` -> `/private/tmp`). A test that gives the
+ * logical path to something that reports paths back — a launched process's
+ * working directory, a bundler's project root — then compares two spellings of
+ * the same directory and fails. Resolving the root once, here, keeps both sides
+ * on the physical path.
+ *
+ * @param {string} prefix - Directory name prefix, e.g. `gev-preview-`.
+ * @returns {Promise<string>} The fixture root, with no symlinked component.
+ */
+export async function makeFixtureRoot(prefix) {
+  return realpath(await mkdtemp(path.join(tmpdir(), prefix)));
+}

src/tooling/fixtureRoot.test.mjs

@@ -0,0 +1,55 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { mkdir, mkdtemp, realpath, rm, symlink } from 'node:fs/promises';
+import { tmpdir } from 'node:os';
+import path from 'node:path';
+import { makeFixtureRoot } from './fixtureRoot.mjs';
+
+// Creating a symlink needs a privilege Windows does not grant by default, and
+// Windows reads its temp directory from other variables than TMPDIR. The case
+// therefore covers macOS and Linux; a Windows equivalent would have to build a
+// directory junction and set TEMP.
+const symlinkTest = process.platform === 'win32' ? test.skip : test;
+
+symlinkTest(
+  'a fixture root is physical even when the temp root is a symlink',
+  async (t) => {
+    // macOS reaches its own temp directory through a symlink and Linux does
+    // not, so build one explicitly: without it this check would pass on the
+    // Linux runner while every Mac contributor still saw the failure it exists
+    // to prevent.
+    const scratch = await realpath(
+      await mkdtemp(path.join(tmpdir(), 'gev-fixture-root-')),
+    );
+    t.after(() => rm(scratch, { recursive: true, force: true }));
+    const physical = path.join(scratch, 'physical');
+    const viaLink = path.join(scratch, 'link');
+    await mkdir(physical);
+    await symlink(physical, viaLink);
+
+    const before = process.env.TMPDIR;
+    process.env.TMPDIR = viaLink;
+    t.after(() => {
+      if (before === undefined) delete process.env.TMPDIR;
+      else process.env.TMPDIR = before;
+    });
+    // Fail rather than pass vacuously: if the temp root is not the symlink,
+    // the condition under test was never set up.
+    assert.equal(
+      tmpdir(),
+      viaLink,
+      'the symlinked temp root was not in force, so nothing was exercised',
+    );
+
+    const root = await makeFixtureRoot('gev-fixture-case-');
+    assert.equal(
+      root,
+      await realpath(root),
+      'the fixture root still contains a symlink',
+    );
+    assert.ok(
+      root.startsWith(`${physical}${path.sep}`),
+      `${root} is not under the physical temp root ${physical}`,
+    );
+  },
+);

src/tooling/previewServing.test.mjs

@@ -1,11 +1,11 @@
 import assert from 'node:assert/strict';
 import test from 'node:test';
-import { mkdtemp, writeFile, rm } from 'node:fs/promises';
-import { tmpdir } from 'node:os';
+import { writeFile, rm } from 'node:fs/promises';
 import path from 'node:path';
 import { build, createServer, preview } from 'vite';
 import { localProviderPlugins } from '../../server/providers/local.js';
 import { apiNotFoundPlugin } from '../../server/standalone/api-not-found.js';
+import { makeFixtureRoot } from './fixtureRoot.mjs';
 
 test('data providers have both hooks; credential editing stays development-only', () => {
   for (const plugin of localProviderPlugins()) {
@@ -27,7 +27,9 @@ test('data providers have both hooks; credential editing stays development-only'
 });
 
 test('real dev and built-preview servers serve provider JSON and terminate unknown APIs', async (t) => {
-  const root = await mkdtemp(path.join(tmpdir(), 'gev-preview-'));
+  // Physical path: Vite's root and the files written under it must agree on one
+  // spelling, and macOS reaches the temp directory through a symlink.
+  const root = await makeFixtureRoot('gev-preview-');
   t.after(() => rm(root, { recursive: true, force: true }));
   await writeFile(
     path.join(root, 'index.html'),