Hacker News Reader

> How do you make sure that the refactored class does the same thing as the old one?

This. This is the problem. The answer, with tests.

What properties do you write tests for, though? Presumably you're touching the code because there's something wrong with it. How do you know how much of it is wrong? How do you know that all callers are actually thinking the current behavior is wrong, instead of one caller misbehaving and another caller expecting it (possibly because someone noticed and worked around it, and now that workaround is going to break)?

Tests are simply the implementation of knowing what the code is expected to do. If you don't have any basis for that expectation, writing tests is meaningless - either you test the current behavior of the code, which doesn't help you change anything, or you test your imagined behavior of the code, which doesn't help you validate anything.

I agree, and commend how well you've noted the problems when code is written without tests. Such a codebase becomes mentally exhausting and expensive to probe into; much more expensive than the original time saved by ignoring testing practices altogether. Sure, a huge amount of legacy software may not have tests, let alone comments. Then yes, it's like where do you even begin and have any confidence in what youre testing for. But ignoring proper testing practices in new, modern codebases, especially in a business where the single product or service offering is software, is extremely risky and irresponsible. This is a little ranty because why are devs justifying not writings tests in 2018!

Reply on news.ycombinator.com