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Comment by ww520 | Hacker News Reader

For service directory lookup, global variable is fine. For global scope queue, global variable is fine. For global scope logging service, global variable is fine.

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Each of these things prevents isolated testing of dependent components. For that reason alone they are nonstarters.

   globalvar = new NopImpl()

works fine for testing. If you squint, you can even think of dependency injection frameworks like Dagger as a lot of boilerplate around a global database of instantiations.

Until you try to run two tests at once, one which requires NopImpl and one which requires the real impl.

As dcow pointed out, it really doesn't work fine for testing, as it couples what should be isolated tests together, and prevents them from being executed concurrently.

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