You don't inject for tests

I think through out the whole discussion about DI in the past week or so is that people don't talk about the injectors themselves enough. Too many pseudo-experts talking about inconsequential and totally unrelated programming principles and paradigms.

I don't think people naturally object to coding to the interface, which this example illustrates very well its utility. I think detractors simply just hate the injectors, the people who use the bad injectors indiscriminately, and the stubborn people who insist on doing DI on an entire app.

My guess is, most people automatically jump to a DI framework not really because of DI, you can do DI with just a good old factory and may be a good configuration library. Most people jump to DI because of a framework, and the niceties that said framework offers. After a while, people just start confusing the effect with the cause.

Can we please start talking about what is DI, when would one find it useful, and what DI approach is suitable under what circumstances now?

Red must be the best - it goes the fastest!

In a dynamic language, unit testing is a bad reason to use dependency injection. There are lots of valid reasons to use it. But you don't need it for unit testing.

Returning to DHH's example, if you just want to get the current time in Ruby code, just get it. You can use the dynamic nature of the language to stub that out and unit test it. But you don't need to use dependency injection to enable that. And you really don't need to use a heavy framework.

If you have a different reason to use dependency injection, though, by all means go ahead.

I'm not sure many people argued that it wasn't about maintainability. I'd say they just ignored that part of the argument.

The best explanations of Unit Tests I've seen also explain how it helps improve maintainability, so perhaps that's why Unit Testing and Maintainability has always gone hand-in-hand in my thinking.

Title says: "You don't inject for tests"

And, before opening the link, you know what you're going to find.

Someone confusing "testing" and "unit testing".

First thing that came to my mind (while reading the header on HN) was "There are several kind of testing..." but... Curiosity killed the cat. Let's open the link.

Ouch, first sentence:

"What is unit testing for?"

OK, closed.

Don't waste your time reading this crap ; )