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Comment by hedora | Hacker News Reader

Here are a few mistakes I've seen in other frameworks:

- Make it possible to disable timeouts. Otherwise, people will need a different runner for integration, long running (e.g., find slow leaks), and benchmark tests. At that point, your runner is automatically just tech debt.

- It is probably possible to nest before and afters, and to have more than one nesting per process, either from multiple suites, or due to class inheritance, etc. Now, you have a tree of hooks. Document whether it is walked in breadth first or depth first order, then never change the decision (or disallow having trees of hooks, either by detecting them at runtime, or by picking a hook registration mechanism that makes them inexpressible).

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We recently switched our system to a heartbeat system instead of a timeout system. The testing framework expects to see messages (printf, console.log, etc...) often. So a test testing a bunch of combinations might take 45 seconds to run but for each combination it's printing "PASS: Combination 1, 2, 3" every few ms.

This way the framework can kill the test if it doesn't see one of these messages in a short amount of time.

This fixed our timeout issues. We had tests that took too long, specially in debug builds and we'd end up having to set too large a timeout. Now though, we can keep the timeout for the heartbeat really short and our timeout issues have mostly gone away.

Never disable the timeouts. What you want is a way to set the timeouts once for an entire suite. Unit, functional, and integration tests all have a different threshold from each other. But in general within one kind your outliers almost always have something wrong with them. They’re either written wrong or the code is. And once I’m a while it’s okay to override the timeout on one test while you’re busy working on something else.

The problems isn’t with breaking rules. The problem is with promising yourself or others that you will fix it “later” and then breaking that promise.

I'd add one more: clearly document what determines the order in which tests are run.

On the one hand, running tests in any order should produce the same result, and would in any decent test suite.

On the other hand, if the order is random or nondeterministic, it's really annoying when 2% of PRs randomly fail CI, not because of any change in the code, but because CI happened to run unrelated tests in an unexpected order.

I’ll disagree with this. Every time I’ve seen that, the interference between tests was also possible between requests in production. I’d rather my test framework give me a 2% chance of noticing the bug than 0%.

What's annoying is not being able to reproduce the 2% cases so you can't fix it even when you've noticed them. Sensible test tools give you the random seed they used to order the tests so you can reproduce the sequence.

Test order should be random, so that the ability to run them in parallel and distribute them across multiple hosts is not lost by missing enforcement of test isolation.

> On the one hand, running tests in any order should produce the same result, and would in any decent test suite.

Therefore the tool should run the tests in random order, to flush out the non-decent tests. IMHO.

If you do this, then the tool should be running the tests all the time, not just on new commits.

The Ruby `minitest` API used to have a way to disable non-deterministic test ordering, but it was intentionally named in a condescending way: https://www.rubydoc.info/gems/minitest/Minitest%2FTest.i_suc...!

I sometimes run into issues not so much due to order dependencies specifically, but due to tests running in parallel sometimes causing failures due to races. It's almost always been way more work to convert a fully serial test suite into a parallel one than it is to just write it that way from the start, so I think there's some merit in having test frameworks default to non-deterministic ordering (or parallel execution if that's feasible) with the ability to disable that and run things serially. I'm not dogmatic enough to think that fully parallel/random order tests are the right choice for every possible use case, but I think there's value in having people first run into the ordering/race issues they're introducing before deciding to run things fully serially so that they hopefully will consider the potential future work needed if they ever decide to reverse that decision.

The tests are fatally broken. It means you can't trust them to properly check new work even.

The solution is to use random ordering and print the ordering seed with each run so it can be repeated when it triggers an error. Immediately halt all new work until randomly run tests don't have problems.

This isn't as bad as it sounds, generally it's a few classes of things that cause the interference which each will fix many tests. It's unlikely that the code actually has a 2%+ density of global-variable use, for example.

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