4 ms·

The fact that something might go wrong in the integration test doesn't mean unit tests for the core logic aren't helpful. Besides, you're probably going to be

The fact that something might go wrong in the integration test doesn't mean unit tests for the core logic aren't helpful. Besides, you're probably going to be using an external library for the SFTP connect, so it's very likely to go just fine. And you can totally use unit tests for what I'm describing. Two classes - SFTPHandler. Connects via SFTP, downloads latest files off the server, passes contents as a string to the processor class `FileProcessor.process(downloaded_file)` - FileProcessor. Has one public function, process, which processes the file - doing whatever it needs to. This function can then very easily be unit tested, just passing strings for test files into the function. You can also refactor the `process` function as much as you like, not needing to worry about the SFTP connection at all. The `process` function probably calls a bunch of private functions within that class, but your unit tests don't need to worry about that. I've used a setup like this in production, it works just fine, and allowed us to improve the performance of the file processing logic and make changes to it very easily and often - without worrying about regressions to the core business logic.

candiodari 8y ago
In my experience if there's one thing absolutely guaranteed it's that unit tests decrease the performance of whatever they're testing (Because it eventually leads to local wins that are big losses for the program as a whole, because this encourages doing idiotic stuff like allocating large buffers and keeping enormous non-shared caches and maps) Now in the example given, performance does not matter, so I do wonder why you'd mention it at all. How about you just answer me this question: Did you still see significant bug volumes after implementing the unit tests for the FileProcessor ? Obviously I believe the answer to be "yes". I feel like your statement that changes were made "very easily and often" sort of implies that yes, there were many bugs. Note that testing based on past bugs is not called unit testing. That is, as you might guess, regression testing (and has the important distinction that it's a VERY good practice to go back through your regression tests once a year, and throw out the ones that don't make sense anymore, which should be about half of them) Besides, I've very rarely seen tests actually catch bugs. Bugs come from pieces of code not doing what developers expect them to do in 2 ways : 1) outright lack of understanding what the code does (this can also mean that they understand the code, but not the problem it's trying to solve, and so code and tests ... are simply both wrong) 2) lack of consideration for edge cases 3) lack of consideration for the environment the code runs in (e.g. scaling issues. Optimizing business logic that processes a 10M file then executing it on 50G of data) None of these has a good chance of getting caught by unit tests in my experience. But developers seem to mostly hate integration tests. Tests that start up the whole system, or even multiple copies of it, and then rapidly run past input through the whole system. When it fails, it takes a while to find why it fails. It may fail, despite all components, potentially written by different people, being "correctly written" just not taking each other into account. It may fail because of memory, cpu starvation, filesystem setup. It may fail occassionally because the backend database decided to VACUUM, and the app is not backing off. It may fail after a firmware upgrade on equipment it uses. The problem I have with these "issues" is simple: they represent reality. They will occur in production. And in some ways I feel like this is a fair description: unit tests are about "proving you're right", even, and perhaps especially, if you're wrong. "You see, it isn't my code ! Not my fault !".
- fredifrum 8y ago
  It still seems like the core of your argument is "Some things are hard to test, so you might as well not test anything at all" - which I really don't buy. > How about you just answer me this question: Did you still see significant bug volumes after implementing the unit tests for the FileProcessor ? Kinda tricky to answer this, since there were test for this class from the start. But, overall the answer is "no" - we did not see significant bugs in that class. Occasionally we'd get a bug because the SFTP connection failed, or execution took to long and the connection closed - the type of bug that to you seems to negate the value of uniting testing the FileProcessor. But, without the unit tests for the FileProcessor, I'd have those bugs plus more bugs/bad behavior in the business logic. How is that better, exactly? The idea that tests reduce performance is ridiculous. Improving performance requires making changes to a system while ensuring it's behavior hasn't changed. This is exactly what testing provides. Without tests, you can't optimize the code at all without fear of introducing regressions.
  - candiodari 8y ago
    > It still seems like the core of your argument is "Some things are hard to test, so you might as well not test anything at all" Nope. My argument is twofold: 1) unit tests don't actually provide the guarantees that people keep putting forward as reasons to write them 2) this makes them a dangerous, as they provide "reassurance" that isn't actually backed by reality > But, without the unit tests for the FileProcessor, I'd have those bugs plus more bugs/bad behavior in the business logic. How is that better, exactly? So the tests failed to catch problems with the program's behavior. Maybe it's just me, but I call that a problem. Testing the business logic as a whole is not a unit test, except in the marginal cases where all your business logic fits neatly in a single function, or at least a single class. If it's actually a few algorithms, a few files, a bunch of functions and you test everything together, that's an integration test and not a functional test. If you use actual (or slightly changed) data to test that business logic, as opposed to artificially crafted data, that again makes it not a unit test. > The idea that tests reduce performance is ridiculous If you use tests to optimize code you're optimizing a piece of code in isolation, without taking the rest of the system into account. That works for trivially simple initial optimization, but falls completely on it's face when you're actually writing programs that stress the system. > Improving performance requires making changes to a system while ensuring it's behavior hasn't changed. The system as a whole, sort of. Individual units ? Absolutely not. Besides, tests merely provide FALSE assurance behavior hasn't changed. Time and time again I've had to fix "I've optimized it" bugs. TLDR is always the same. Unit tests pass so the code "must be right" (meaning they don't run the code outside of unit tests, and the unit tests only directly test the code, not blackbox). Then in the actual run edge cases were hit. And "edge cases" makes it sound like you hardly ever hit this. Just yesterday we had a big issue. What happened ? Well we had a method that disables an inbound phone line (e.g. for maintenance, or changes). All unit tests passed. Unfortunately we really should have tested that it does NOT disable anything else (method was essentially "go through list, if it matches, disable". Needless to say, it disabled every line). Regression testing added. We had someone optimize the dial plan handling. He didn't realize that his "cache" was in fact recreated at the very beginning of every request, when the code evaluated a dial plan, in other words, it was a serious performance regression rather than an improvement. Really looked like an improvement though. Unit tests ... passed. Of course, "the behavior hadn't changed". About 2 calls got through for ~6 minutes (normally thousands). Now we have a test that turns up the whole system, with the actual production dial plan, and then goes through 10000 calls. If it takes more than 1 minute, test fails. Developers hate it, but it's non-negotiable at this point. I can go on for quite a while enumerating problems like this. Billing files erased (forgot to append). Entire dialplan erased on startup (essentially same problem). Lots of ways to trigger cpu starvation. Memory exhaustion. Memory leaks (the system is mostly Java). Connecting unrelated calls together (that was pretty fun for the first 2-3 minutes). Ignoring manager signals (one server having to do all calls ... which is not happening) This is a repeating pattern in our failures. Unit tests ... essentially always pass. And time and time again someone tries to make the point that this must mean the code is correct. And that's bullshit. That's the problem.

candiodari 8y ago

In my experience if there's one thing absolutely guaranteed it's that unit tests decrease the performance of whatever they're testing (Because it eventually leads to local wins that are big losses for the program as a whole, because this encourages doing idiotic stuff like allocating large buffers and keeping enormous non-shared caches and maps) Now in the example given, performance does not matter, so I do wonder why you'd mention it at all. How about you just answer me this question: Did you still see significant bug volumes after implementing the unit tests for the FileProcessor ? Obviously I believe the answer to be "yes". I feel like your statement that changes were made "very easily and often" sort of implies that yes, there were many bugs. Note that testing based on past bugs is not called unit testing. That is, as you might guess, regression testing (and has the important distinction that it's a VERY good practice to go back through your regression tests once a year, and throw out the ones that don't make sense anymore, which should be about half of them) Besides, I've very rarely seen tests actually catch bugs. Bugs come from pieces of code not doing what developers expect them to do in 2 ways : 1) outright lack of understanding what the code does (this can also mean that they understand the code, but not the problem it's trying to solve, and so code and tests ... are simply both wrong) 2) lack of consideration for edge cases 3) lack of consideration for the environment the code runs in (e.g. scaling issues. Optimizing business logic that processes a 10M file then executing it on 50G of data) None of these has a good chance of getting caught by unit tests in my experience. But developers seem to mostly hate integration tests. Tests that start up the whole system, or even multiple copies of it, and then rapidly run past input through the whole system. When it fails, it takes a while to find why it fails. It may fail, despite all components, potentially written by different people, being "correctly written" just not taking each other into account. It may fail because of memory, cpu starvation, filesystem setup. It may fail occassionally because the backend database decided to VACUUM, and the app is not backing off. It may fail after a firmware upgrade on equipment it uses. The problem I have with these "issues" is simple: they represent reality. They will occur in production. And in some ways I feel like this is a fair description: unit tests are about "proving you're right", even, and perhaps especially, if you're wrong. "You see, it isn't my code ! Not my fault !".

fredifrum 8y ago
It still seems like the core of your argument is "Some things are hard to test, so you might as well not test anything at all" - which I really don't buy. > How about you just answer me this question: Did you still see significant bug volumes after implementing the unit tests for the FileProcessor ? Kinda tricky to answer this, since there were test for this class from the start. But, overall the answer is "no" - we did not see significant bugs in that class. Occasionally we'd get a bug because the SFTP connection failed, or execution took to long and the connection closed - the type of bug that to you seems to negate the value of uniting testing the FileProcessor. But, without the unit tests for the FileProcessor, I'd have those bugs plus more bugs/bad behavior in the business logic. How is that better, exactly? The idea that tests reduce performance is ridiculous. Improving performance requires making changes to a system while ensuring it's behavior hasn't changed. This is exactly what testing provides. Without tests, you can't optimize the code at all without fear of introducing regressions.
- candiodari 8y ago
  > It still seems like the core of your argument is "Some things are hard to test, so you might as well not test anything at all" Nope. My argument is twofold: 1) unit tests don't actually provide the guarantees that people keep putting forward as reasons to write them 2) this makes them a dangerous, as they provide "reassurance" that isn't actually backed by reality > But, without the unit tests for the FileProcessor, I'd have those bugs plus more bugs/bad behavior in the business logic. How is that better, exactly? So the tests failed to catch problems with the program's behavior. Maybe it's just me, but I call that a problem. Testing the business logic as a whole is not a unit test, except in the marginal cases where all your business logic fits neatly in a single function, or at least a single class. If it's actually a few algorithms, a few files, a bunch of functions and you test everything together, that's an integration test and not a functional test. If you use actual (or slightly changed) data to test that business logic, as opposed to artificially crafted data, that again makes it not a unit test. > The idea that tests reduce performance is ridiculous If you use tests to optimize code you're optimizing a piece of code in isolation, without taking the rest of the system into account. That works for trivially simple initial optimization, but falls completely on it's face when you're actually writing programs that stress the system. > Improving performance requires making changes to a system while ensuring it's behavior hasn't changed. The system as a whole, sort of. Individual units ? Absolutely not. Besides, tests merely provide FALSE assurance behavior hasn't changed. Time and time again I've had to fix "I've optimized it" bugs. TLDR is always the same. Unit tests pass so the code "must be right" (meaning they don't run the code outside of unit tests, and the unit tests only directly test the code, not blackbox). Then in the actual run edge cases were hit. And "edge cases" makes it sound like you hardly ever hit this. Just yesterday we had a big issue. What happened ? Well we had a method that disables an inbound phone line (e.g. for maintenance, or changes). All unit tests passed. Unfortunately we really should have tested that it does NOT disable anything else (method was essentially "go through list, if it matches, disable". Needless to say, it disabled every line). Regression testing added. We had someone optimize the dial plan handling. He didn't realize that his "cache" was in fact recreated at the very beginning of every request, when the code evaluated a dial plan, in other words, it was a serious performance regression rather than an improvement. Really looked like an improvement though. Unit tests ... passed. Of course, "the behavior hadn't changed". About 2 calls got through for ~6 minutes (normally thousands). Now we have a test that turns up the whole system, with the actual production dial plan, and then goes through 10000 calls. If it takes more than 1 minute, test fails. Developers hate it, but it's non-negotiable at this point. I can go on for quite a while enumerating problems like this. Billing files erased (forgot to append). Entire dialplan erased on startup (essentially same problem). Lots of ways to trigger cpu starvation. Memory exhaustion. Memory leaks (the system is mostly Java). Connecting unrelated calls together (that was pretty fun for the first 2-3 minutes). Ignoring manager signals (one server having to do all calls ... which is not happening) This is a repeating pattern in our failures. Unit tests ... essentially always pass. And time and time again someone tries to make the point that this must mean the code is correct. And that's bullshit. That's the problem.