DI is a very religious concept, people hate it or love it. I myself am on the dislike camp, I have found that mocking modules (like you can with NodeJS testing

DI is a very religious concept, people hate it or love it. I myself am on the dislike camp, I have found that mocking modules (like you can with NodeJS testing frameworks) for tests gives most of the benefits with way less development hell. However you do need to be careful with the module boundaries (basically structure them as you would with DI) otherwise you can end up with a very messy testing system. The value of DI is also directly proportional to the size of the service being tested, DI went into decline as things became more micro-servicy with network-enforced module boundaries. People are just mocking external services in these kind of codebases instead of internal modules, which makes the boundaries easier. I can see strict DI still being useful in large monolith codebases worked by a lot of hands, if only to force people to structure their modules properly.