I've done DI many times for things other than tests - swapping out different algorithms is the most common case (BetaBanditCalculator -> TimeVaryingBayesianBan

I've done DI many times for things other than tests - swapping out different algorithms is the most common case (BetaBanditCalculator -> TimeVaryingBayesianBanditCalculator -> HierarchicalPersonalCharacteristicCalculator, etc). It also makes testing easy, which is great, but that's far from the only use case. DI tends to work great for the integration point between systems - e.g., connecting the REST or Thrift interface to the calculation backend and datastore. The fact that a concept is hard to use in Enterprise Java is a poor argument against anything other than Enterprise Java.