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.
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.
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.
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.
I respectfully disagree. Not with the last part, that is true: they do bring value under pretty much all circumstances. But the first. Because integration tests come with (extremely) high costs.
They are expensive to run. They are much harder (costlier) to write. They are even harder (costlier) to maintain. The common pushback against tests -but they slow down our team a lot- applies to integration tests much more than to unit tests - factors more. And so on.
As with everything software-engineering, choosing what tests to write is a tradeoff. And taking all into consideration, e2e or integration tests are often not worth their investment¹. The testing pyramid fixes this, because testing always (well- it depends) is worth the investment. But when you skew the testing pyramid, or worse, make it an testing-ice-cream-cone, that ROI can and will often quickly become negative.
¹Edit: I meant to say that many of these e2e tests are not worth their investment. Testing edge-cases for example: if you need man-hours to write a regression test e2e style and then man-weeks to maintain and run that over coming years, it's often better ROI to just let that regression re-appear and have customers report it. Whereas a unit-test that captures this edge-case costs maybe an hour to write, milliseconds to run and hardly any time to maintain.
Unit tests usually have lower capex and higher opex. It often takes less time and effort to write a single lower level unit test but that test will require more frequent maintenance as the code around it evolves due to refactoring.
Integration often tests have higher capex because they rely upon a few complex integration points - e.g. to set up a test to talk to a faux message queue takes time. Getting playwright set up takes quite a chunk of up front time. Building an integration with a faux SMTP endpoint takes time. What is different is that these tools are a lot more generic so it's easier to stand on the shoulders of others and they are more reusable and it's easier to leverage past integrations to write future scenarios. E.g. you don't have to write your own playwright somebody already did that and once you have playwright integrated into your framework any web-related steps on future scenarios suddenly become much easier to write.
Whereas with unit tests the reusability of code and fixtures written in previous tests is generally not as high.
You have to also take into account the % of false negatives and false positives.
I find unit tests often raise more false positives because ordinary legitimate refactoring that introduced no bugs is more likely to break them. This reduces the payoff because you will have more ongoing test failures requiring investigation and maintenance work to mitigate this.
I also find that the % of false negatives is lower. This is harder to appreciate because you wouldn't ever expect, for instance, a unit test to catch that somebody tweaked some CSS that broke a screen or broke email compatibility with outlook, but these are still bugs and they are bugs that integration tests at a high level can catch with appropriate tooling but unit tests will never, ever, ever catch.
>But when you skew the testing pyramid, or worse, make it an testing-ice-cream-cone, that ROI can and will often quickly become negative.
The pyramid is an arbitrary shape that assumes a one size fits all approach works for all software. I think it is one of the worst ideas to ever grace the testing community. What was particularly bad was Google's idea that flakiness should be avoided by avoiding writing tests and applying good engineering practices to root out the flakiness. It was an open advertisement that they were being hampered by their own engineering capabilities.
I do agree that this is a cost/benefit calculation and if you shift some variable (e.g. E2E test tooling is super flaky and you've got good, stable abstractions to write your unit tests against, you've got a lot of complex calculations in your code), then that changes the test level payoff matrix, but I find that the costs and benefits work out pretty consistently to favor integration tests these days.
"more frequent" is not the same as "high maintenance costs" though.
Unit tests should only change when the unit-under-test (sut) changes. Which, for many units is "never". And for some with high churn, indeed, a lot.
Actual and pure e2e tests should never have to change except when the functionality changes.
But all other integration tests most often change whenever one of the components changes. I've had situations where whenever we changed some relation, or added a required-field in our database, we had to manually change hundreds of integration tests and their helpers. "Adding a required field" then became a chore of days of wading through integration tests¹.
With the unit-tests, only one, extremely simple test changed in that case. With the end-to-end-tests, also, hundreds needed manual changes. But that was because they weren't actual end-to-end tests, and did all sorts of poking around in the database. Worse: that poking-around wasn't abstracted even.
What I'm trying to convey with this example, is that in reality, unit-tests change often if the SUT has a high churn, but that those changes are very local and isolated and simple. Yet, in practice, with integration-tests, the smallest unrelated change to a "unit" has a domino-effect on whole sections of these tests. (And also that in this example, our E2E were badly designed and terribly executed)
¹Edit: one can imagine the pressure of management to just stop testing.
- A unit test is single responsibility. It tests just that one bit of code with all dependencies stubbed, abstracted, mocked, or removed from consideration in some way.
- An integration test is multiple responsibility. It tests just one bit of functionality as a vertical slice through the stack (including [only] relevant dependencies) with all other aspects of the code base eliminated from consideration.
- An end to end test is full responsibility. It tests a complete path through all the functionality necessary to complete a 'journey' as a user/consumer of the app/tool.
So for example VAT calculation is unit tested as isolated code, invoicing is integration tested as a vertical slice including database etc, and order processing is end-to-end tested from placing the order through to its completion.
That's a simplified example and not always accurate depending upon the system and the team perspectives/opinions, but the principle of looking at responsibilities is a very useful rule of thumb.
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.
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.
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.
That's why you separate them: not because the integration test isn't valuable, but because it takes longer.