最近在看《Python 测试驱动开发：使用 Django、Selenium 和 JavaScript 进行 Web 编程 (第 2 版)》，运行的时候报错了，请问应该怎么解决
django.core.exceptions.ImproperlyConfigured: Requested setting DATABASES, but settings are not configured. You must either define the environment variable DJANGO_SETTINGS_MODULE or call settings.configure() before accessing settings.