Why Most Unit Testing is Waste [pdf]

From the paper: "Throw away tests that haven’t failed in a year." Hell, no. Our unit tests provide reassurance that when somebody revisits a component N years from now, and makes a change, they are significantly less likely to break the existing behaviour, even subtly. Throwing away unit tests is like saying "This ship has been sailing for years and has never sunk - let's throw away the lifeboats!" Now, yes - somebody could erroneously change the test condition to…

The normal practice for large scale codebases in complex domains is "the code is the spec". That is, the only specification for how the system should work is how it worked yesterday. In that case, unit tests serve as a great specification. Even tests that just duplicate the business code under test and assert that it's the same (A huge waste in normal cases) is useful. Because a Unit test is much better than a word document in describing how…

My experience with testing is like that old adage about advertising, "I know I'm wasting 50% of my money but I don't know which 50%." Most of it is a waste but it's hard to know in advance which test will stop an engineer in a couple of years from altering some fundamental contract and bringing the system down.

> If you want to reduce your test mass, the number one thing you should do is look at the tests that have never failed in a year and consider throwing them away. They are producing no information for you — or at least very little information. The value of the information they produce may not be worth the expense of maintaining and running the tests. This seems.. entirely unreasonable to me. Just because some area of code is not…