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Tests != TDD. TDD encourages an architecture with lots of indirection so that it can achieve the necessary polymorphism for injecting dependencies in test. I c

Tests != TDD. TDD encourages an architecture with lots of indirection so that it can achieve the necessary polymorphism for injecting dependencies in test. I can assure you the linux kernel is not TDD'ed.

wpietri 5y ago
I think that's typically true, but that's because most TDD is done in languages where there's not a lot of cost for indirection. I expect we'd see a different outcome if something like a kernel were started with a TDD approach. For example, we might see ways of expressing indirection for testing that then get removed when building the final product. Or we can look at the great strides made in virtualization since the Linux kernel was started. Something previously hard to test becomes much easier. And I'd expect more so if the testing had co-evolved. Of course, there still might be hard-to-test areas. But given the massive ingenuity applied to the kernel development process over the years, I expect that they would have advanced what's possible in TDD if they had pursued it.
- chitowneats 5y ago
  Why do you think that linux kernel developers have not changed their approach? TDD is not a new idea. If indeed they have continued for decades to do it "the wrong way", imposing costs onto the project and society proportional to the number of preventable bugs creeping in, is this not a major scandal for the industry? I suspect that the core team have reasons that they have not developed tooling to enable TDD of the Linux kernel. And that those reasons are more substantive than "meh".
  - wpietri 5y ago
    TDD is not a new idea, but it's about 10 years newer than the Linux kernel. My experience is that projects very rarely make a switch like the one described by the Factorio team, so I assumed the Linux folks haven't. If you're saying they do work in a TDD fashion, I'm happy to take your word for it.
dnautics 5y ago
> TDD encourages an architecture with lots of indirection so that it can achieve the necessary polymorphism for injecting dependencies in test. This is a language/library thing. Some language/libraries let you do TDD with very little indirection, a table of mocked dependencies as compile-time configuration, and all of the mocking events happen in code in your tests.

wpietri 5y ago

I think that's typically true, but that's because most TDD is done in languages where there's not a lot of cost for indirection. I expect we'd see a different outcome if something like a kernel were started with a TDD approach. For example, we might see ways of expressing indirection for testing that then get removed when building the final product. Or we can look at the great strides made in virtualization since the Linux kernel was started. Something previously hard to test becomes much easier. And I'd expect more so if the testing had co-evolved. Of course, there still might be hard-to-test areas. But given the massive ingenuity applied to the kernel development process over the years, I expect that they would have advanced what's possible in TDD if they had pursued it.

chitowneats 5y ago
Why do you think that linux kernel developers have not changed their approach? TDD is not a new idea. If indeed they have continued for decades to do it "the wrong way", imposing costs onto the project and society proportional to the number of preventable bugs creeping in, is this not a major scandal for the industry? I suspect that the core team have reasons that they have not developed tooling to enable TDD of the Linux kernel. And that those reasons are more substantive than "meh".
- wpietri 5y ago
  TDD is not a new idea, but it's about 10 years newer than the Linux kernel. My experience is that projects very rarely make a switch like the one described by the Factorio team, so I assumed the Linux folks haven't. If you're saying they do work in a TDD fashion, I'm happy to take your word for it.

dnautics 5y ago

> TDD encourages an architecture with lots of indirection so that it can achieve the necessary polymorphism for injecting dependencies in test. This is a language/library thing. Some language/libraries let you do TDD with very little indirection, a table of mocked dependencies as compile-time configuration, and all of the mocking events happen in code in your tests.