5 ms·

From Working Effectively With Legacy Code by Feathers, p. 14[0]: Unit tests run fast. If they don’t run fast, they aren’t unit tests. Other kinds of tests oft

• brightball 3y ago
  That's a great rule of thumb.
• atticora 3y ago
  My "unit tests" do hit the database and file system, and I have found and fixed many many problems during testing by doing so. I have found many other problems with those calls in production when I didn't do so. Yes, they make testing a lot slower. Our main app takes around 40 minutes to build which isn't good. I'd like it to be faster. But writing a bunch of separate integration tests to cover those functions would be a steep price. I can understand reasonable people choosing either approach.
  • berkes 3y ago
    > My "unit tests" do hit the database and file system, and I have found and fixed many many problems during testing by doing so. I have found many other problems with those calls in production when I didn't do so. No-one said that integration tests can't also be very valuable. From the little context I get that you write integration tests, and that is fine. They are useful, valuable! But they are not unit-tests. edit: on re-reading, I get the feeling that for you "integration tests" are a synonym for "end to end tests". But -at least in most literature- end-to-end tests are a kind of integration-test. But not all integration tests are end-to-end tests. In my software, I'll often have integration tests that swap out some adapter (e.g. the postgres-users-repository, for the memory-users-repository, or fake-users-repository. Or the test-payment for the stripe-payment) but that still test a lot of stuff stacked on top of each-other. Integration tests, just not integration tests that test the entire integration.
    • lokar 3y ago
      And integration tests can also be fast
      • alemanek 3y ago
        Test containers really help with this. Should still have the big system tests that run overnight but a set of integration tests using Test Containers to stand in for the infrastructure dependencies is awesome. My team has a ton of those and they run inside a reasonable time frame (5min or so) but we still allow for excluding those from test runs so you can run just the unit tests.
        • darkteflon 3y ago
          I hadn’t heard of Test Containers[1], but it looks really useful - thanks for the rec. [1] https://testcontainers.com/ https://testcontainers.com/
      • berkes 3y ago
        Indeed! It's one of the reasons I like the adapter pattern (aka hexagonal architecture) so much. Data flowing through some 100 classes and 300 conditionals then into a `memory-payments` and back takes mere milliseconds. "Memory payments" is then some silly wrapper around a hashmap with the same API as the full-blown production payments-adapter that calls stripe over HTTP. Or the same api as the "production adapter" that wraps some RDBMS running on the other end of the data-center.
    • MoreQARespect 3y ago
      >No-one said that integration tests can't also be very valuable. Integration tests are a better kind of default test because they bring value under pretty much all circumstances. Nobody said that unit tests cant also be valuable and under just the right circumstances i.e. - complex stateless code behind a stable API. Unit tests shine in that environment - theyre not impeded by their crippling lack of realism because that stable abstraction walls off the rest of reality. And theyre very fast. Most code isnt parsers, calculation engines, complex string manipulation, etc. - but when it is unit tests really do kick ass. They just suck so badly at testing code that doesnt fit that mold. Which, to be fair, is most code. I dont write a lot of parsers at work. My job involes moving data into databases, calling APIs, linking up message queues, etc.
  • fesc 3y ago
    What would "integration tests" (that you don't write) look then in your opinion? I ask because in my team we also a long time made the destinction between unit/integration based on a stupid technicality in the framework we are using. We stopped doing that and now we mostly write integration tests (which in reality we did for a long time). Of course this all arguing over definitions and kind of stupid but I do agree with the definition of the parent commenter.
    • atticora 3y ago
      > What would "integration tests" (that you don't write) look then in your opinion? In our local lingo, an integration test is one that also exercises the front-end, while hitting a fully functional back-end. So you could think of our "unit tests" as small back-end integration tests. If you think that way, we don't write very many pure unit tests, mostly just two flavors of integration tests. That works well for our shop. I'm not concerned about the impurity.
      • ebiester 3y ago
        The "impurity" isn't the problem. The problem is that such integration tests take a longer time to run and in aggregate, it takes minutes to run your test suite. This changes how often you run your tests and slows down your feedback loop. That's why you separate them: not because the integration test isn't valuable, but because it takes longer.
  • gbacon 3y ago
    No one suggests discarding integration tests. The end of the quoted excerpt from Feathers above explicitly supports them. Tests that do these things aren’t bad. Often they are worth writing, and you generally will write them in unit test harnesses. You hinted at the value of separating unit tests and integration tests with your observation about 40-minute unit test runs being way too slow. The process friction it creates means people will check in “obviously correct” changes without running the tests first. Feathers continues: However, it is important to be able to separate them from true unit tests so that you can keep a set of tests that you can run fast whenever you make changes. You want your unit tests to be an easy habit for a quick sanity check. For the situation you described, I’d suggest moving the integration tests to a separate suite that run at least once a day. Ripping that coverage out of your CI may make you uncomfortable. That’s solid engineering intuition. Let your healthy respect for the likelihood of errors creeping in drive you to add at least one fast (less than one-tenth of a second to run is the rule of thumb from Feathers, p. 13) test in the general area of the slower integration tests. The first one may be challenging to write. From here forward, it will never be easier than today. Putting it off is how your team got to the situation now of having to wait 40 minutes for the green bar. One test is better than no tests. Your first case with the fixture and mocks you create will make adding more fast unit tests easier down the road. Yes, just as it’s possible to make mistakes in production code, it’s certainly possible to make mistakes in test code. Unit tests are sometimes brittle and over-constrain. Refactoring them is fair game too and far better than throwing them away.
• deleted 3y ago
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• randomdata 3y ago
  In other words, unit tests – unless, perhaps, you count an empty test as being a unit test – do not exist. "Talking" to structured sets of data, i.e. a database, is fundamental to computing.
• jcranmer 3y ago
  I'd actually quibble a lot on this definition--if you want to unit test code that needs to do any of the first three things, well, you have to do them to test the code. I would say that a test for a network protocol that works by spinning up an echo server on a random port and having the code connect to that echo server is still a unit test for that network protocol. In my definition, it would still be a unit test if it is fast and it talks to a database, a network server, or the file system, so long as such communication is done entirely in a "mock" fashion (it only does such communication as the test sets up, and it's done in such a fashion that tests can be run in parallel with no issues).
• dllthomas 3y ago
  I've never liked the conflating of target size and test time constraints. I very much agree that there's benefit to considering the pace of feedback and where it falls in your workflow; immediate feedback is hugely valuable, but it can come from unit tests, other tests, or things which are not tests. Meanwhile, some tests of a single unit might have to take a long time. Exhaustive tests are rarely applicable, but when they are it's going to be for something small and it's likely to be slow to run. That should not be in your tightest loop, but it is probably clearer to evict it simply because it is slow, rather than because it is not a unit test for being slow.
• closeparen 3y ago
  It is pretty excruciating (and IMO useless) to write true, DB-isolated unit tests for DB access layer code.
• physicles 3y ago
  I haven't found the distinction between unit tests and non-unit tests to be that useful in practice. The important questions are: 1. Is it kinda slow? (The test suite for a single module should run in a few seconds; a large monorepo should finish in under a minute) 2. Is there network access involved? (Could the test randomly fail?) 3. Do I need to set up anything special, like a database? (How easy is it for a new developer to run it?) If the answer to any of those is Yes, then your test might fall in the liminal space between unit tests and integration tests -- they're unit-level tests, but they're more expensive to run. For example, data access layer tests that run against an actual database. On the other hand, even if a test touches the filesystem, then it's generally fast enough that you don't have to worry about it (and you did make the test self-cleaning, right?) -- calling that test "not a unit test" doesn't help you. Likewise, if the database you're touching is sqlite, then that still leaves you with No's to the three questions above.
• _dain_ 3y ago
  >1. It talks to a database. >3. It touches the file system. These are BS. Maybe they made sense in the beforetimes when when we didn't have Docker containers or SSDs, but nowadays there's no reason you can't stand up a mini test database as part of your unit test suite. It's way simpler than mocking.
  • icedchai 3y ago
    100% this. A guy I work with just rebuilt our CI/CD pipeline and we're spinning up a database and all dependent services in containers. There are no mocks and it works great. In previous lives, I worked on tests that mocked everything. We spent more time creating and maintaining mocks than writing the actual tests.
    • nerdponx 3y ago
      I think those are still considered "integration" tests in the traditional way of thinking. The problem is that a lot of applications don't do much other than interact with external resources, to the point where isolated unit tests are rare or only cover non-critical code, while just about any substantive test is an "integration" test.
      • icedchai 3y ago
        Yes, you are correct. I never cared much for the traditional way of thinking about tests. I've had more arguments with people claiming this is an integration test, not a unit test, write some mocks, etc. Outside of very specific pieces of code, you generally get more value from integration tests.
• munksbeer 3y ago
  I've dropped my archaic thinking on what constitutes a unit test or an integration test. I now seldom write what most people consider unit tests, in the "one class, one test" sense. Instead, I classify units of logical coherence and write unit tests for those. I write financial trading systems - not hft, but still latency sensitive. I will test an order through our pipeline as a unit of work. This will necessarily touch multiple classes. So as an example, a test will cover orders which are accepted and then filled, orders which are rejected, and so on. Many people would classify these as integration tests, and to be fair, I don't really care what you name them. To me these are much more valuable than the traditional "one class, one test" mechanism because it means I am free to refactor the internals of our pipeline as much as I want with very low impact on the test code. One of the whole points of test code, that I think has been lost, is that it should be there to give you confidence in the correctness of your application under change. Writing "one class, one test" is a bad way to achieve this.