ENG-219: Add createTempProject helper for test isolation

Tests that modify .puprc now use isolated temp directories instead of
the shared fixture directory, allowing parallel test execution.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: d4mation

tests/commands/invalid-puprc.test.ts

@@ -1,22 +1,28 @@
 import {
   runPup,
-  resetFixtures,
-  fakeProjectDir,
+  createTempProject,
+  cleanupTempProjects,
 } from '../helpers/setup.js';
 import fs from 'fs-extra';
 import path from 'node:path';
 
 describe('invalid .puprc', () => {
+  let projectDir: string;
+
+  beforeEach(() => {
+    projectDir = createTempProject();
+  });
+
   afterEach(() => {
-    resetFixtures();
+    cleanupTempProjects();
   });
 
   it('should handle invalid JSON in .puprc', async () => {
-    const puprcPath = path.join(fakeProjectDir, '.puprc');
+    const puprcPath = path.join(projectDir, '.puprc');
     fs.writeFileSync(puprcPath, '{invalid json}');
 
-    const result = await runPup('info');
+    const result = await runPup('info', { cwd: projectDir });
     // Should still run but report invalid config
-    expect(result.stdout + result.stderr).toBeTruthy();
+    expect(result.output).toContain('could not be parsed');
   });
 });

tests/helpers/setup.ts

@@ -1,4 +1,5 @@
 import path from 'node:path';
+import os from 'node:os';
 import { execFile } from 'node:child_process';
 import fs from 'fs-extra';
 
@@ -10,6 +11,7 @@ export const fakeProjectWithTbdsDir = path.resolve(fixturesDir, 'fake-project-wi
 export const cliPath = path.resolve(pupRoot, 'dist', 'cli.js');
 
 const tempFiles: string[] = [];
+const tempDirs: string[] = [];
 
 export function getDefaultPuprc(): Record<string, unknown> {
   return {
@@ -85,6 +87,38 @@ export function runPup(
   });
 }
 
+/**
+ * Creates an isolated copy of a fixture directory in a temp location.
+ *
+ * @since TBD
+ *
+ * @param {string} fixture - The fixture directory name to copy (e.g. 'fake-project').
+ *
+ * @returns {string} The path to the isolated temp directory.
+ */
+export function createTempProject(fixture = 'fake-project'): string {
+  const tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), `pup-test-${fixture}-`));
+  fs.copySync(path.resolve(fixturesDir, fixture), tmpDir);
+  tempDirs.push(tmpDir);
+  return tmpDir;
+}
+
+/**
+ * Removes all temp directories created by createTempProject.
+ *
+ * @since TBD
+ *
+ * @returns {void}
+ */
+export function cleanupTempProjects(): void {
+  for (const dir of tempDirs) {
+    if (fs.existsSync(dir)) {
+      fs.removeSync(dir);
+    }
+  }
+  tempDirs.length = 0;
+}
+
 export function resetFixtures(): void {
   // Remove any .puprc files we wrote
   for (const f of tempFiles) {