Method createTestDir

test/lib/next-modes/base.ts:220–492

({
    skipInstall = false,
    parentSpan,
  }: {
    skipInstall?: boolean
    parentSpan: Span
  })

  }

  protected async createTestDir({
    skipInstall = false,
    parentSpan,
  }: {
    skipInstall?: boolean
    parentSpan: Span
  }) {
    if (this.isDestroyed) {
      throw new Error('next instance already destroyed')
    }

    await parentSpan
      .traceChild('createTestDir')
      .traceAsyncFn(async (rootSpan) => {
        const skipIsolatedNext = !!process.env.NEXT_SKIP_ISOLATE
        if (!skipIsolatedNext) {
          require('console').log(
            `Creating test directory with isolated next... (use NEXT_SKIP_ISOLATE=1 to opt-out)`
          )
        }
        const tmpDir = skipIsolatedNext
          ? path.join(__dirname, '../../tmp')
          : process.env.NEXT_TEST_DIR || (await fs.realpath(os.tmpdir()))
        this.testDir = path.join(
          tmpDir,
          `next-test-${Date.now()}-${(Math.random() * 1000) | 0}`,
          this.subDir
        )
        this.distDir = getDistDir()

        const reactVersion =
          process.env.NEXT_TEST_REACT_VERSION || nextjsReactPeerVersion
        const finalDependencies = {
          react: reactVersion,
          'react-dom': reactVersion,
          '@types/react': '19.2.2',
          '@types/react-dom': '19.2.1',
          typescript: 'latest',
          '@types/node': 'latest',
          ...this.dependencies,
          ...this.packageJson?.dependencies,
        }

        if (
          process.env.__NEXT_ENABLE_REACT_COMPILER === 'true' &&
          !finalDependencies['babel-plugin-react-compiler']
        ) {
          finalDependencies['babel-plugin-react-compiler'] =
            '0.0.0-experimental-3fde738-20250918'
        }

        if (skipInstall || skipIsolatedNext) {
          const pkgScripts = (this.packageJson['scripts'] as {}) || {}
          await fs.mkdir(this.testDir, { recursive: true })
          await fs.writeFile(
            path.join(this.testDir, 'package.json'),
            JSON.stringify(
              {