新增于: v18.0.0
TestContext 的实例被传给每个测试函数，以便与测试运行器交互。
但是，TestContext 构造函数没有作为 API 的一部分公开。
Added in: v18.0.0
An instance of TestContext is passed to each test function in order to
interact with the test runner. However, the TestContext constructor is not
exposed as part of the API.