之前有一个奋斗了 N 小时才搞定的问题，在 Nestjs 的单元测试中反复测试会报类似于：
Starting Nest throws following error: Nest can't resolve dependencies of the EventResolver (EventService, ?). Please make sure that the argument at index  is available in the EventModule context.
Nest throws an error about a circular dependency that doesn't exist. Here is the error thrown: Nest cannot create the module instance. Often, this is because of a circular dependency between modules. Use forwardRef() to avoid it. (Read more https://docs.nestjs.com/fundamentals/circular-dependency.) Scope [RootModule -> XXXModule]