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Comment by mekazu | Hacker News Reader

Unit tests that don’t read or write to disk and don’t try thousands of repetitions of things should be bleeding fast, but the most useful integration tests that actually help find faults (usually with your assumptions about the associated APIs) often need interaction with your disk or database or external service and tend to take a bit more than a few seconds. I find you need both.

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I have tests which verify DNA analysis. The test data vectors are large -- a few hundred MB here, a couple GB there. The hundreds of tests that use these test vectors still run in a few seconds.

If you're using a tape drive or SD cards, sure. But even a 10 year old 5400RPM on an IDE connection should be able to satisfy your tests' requirements in a few seconds or less.

I suspect your tests are just as monolithic as you think microservices shouldn't be. Break them down into smaller pieces. If it's hard to do that, then redesign your software to be more easily testable. Learn when and how to provide static data with abstractions that don't let your software know that the data is static. Or, if you're too busy, then hire a dedicated test engineer. No, not the manual testing kind of engineer. The kind of engineer who actually writes tests all day, has written thousands (or hundreds of thousands) of individual tests during their career. And listen to them about any sort of design decisions.

Sounds like you have tests that need to read (probably cached) data files while the parent poster has tests that need to write to disks (probably in a database transaction). Those are different enough that run times won't ever be comparable.

I have tests that need to read. I have tests that need to write. All data written must also be read and verified. You're right, the data is probably cached.

If you need to access a database in your tests you're probably doing it wrong. Build a mock-up of your database accessor API to provide static data, or build a local database dedicated for testing.

Sure. I'd venture to say that integration tests should be fewer than unit tests, see hexagonal etc. Hopefully those external interfaces are also more stable, so they don't need to be run as often.

I tend to use my integration tests also as characterization tests that verify the simulator/test-double I use for any external systems within my unit tests.

See also: the testing pyramid[1] and "integrated tests are a scam"[2], which is a tad click-bait, but actually quite good.

[1] https://martinfowler.com/bliki/TestPyramid.html

[2] https://www.youtube.com/watch?v=VDfX44fZoMc

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