> - If you want to know if your utility classes and functions are sane, unit testing is far better bang for your buck than trying to figure out whether they're being adequately exercised in your service tests.

I think we talk about the same thing, sometimes I will test something internal.

I've thought about what I'm doing as considering larger "units" in my unit testing, but perhaps "functional testing" as parent introduced is what I'm advocating. I see this as distinct from integration testing. In a micro service architecture, my integration test would be chaining multiple services together into test scenarios.

I'm kind of flexible on my terminology, perhaps more flexible than others, since my approach to testing has largely been self-taught from the experience of several shops.

To me, unit tests are when I'm testing the behavior of a "thing" in "isolation", for some definitions of those terms – and yes, I agree that those definitions vary greatly. However, I don't agree with you that the flexibility of the definition is an issue.

Integration testing for me is when I'm testing system interfaces, so I'm focusing on how my systems behave when they come together. Sometimes I do this in isolation, using stub services or even internal stubs to simulate another system's behavior, but generally I do it with an actual system when it's convenient.

I don't generally use the term functional testing because I personally think it's ambiguous – I'm testing functionality in either case! But I suspect our differences really just boil down to how you slice it. If you prefer to divide tests into black-box vs white-box, but don't care as much about the specific level of isolation involved in the test, functional testing is perhaps the term you'd prefer. I prefer to categorize tests in terms of the amount of isolation I'm using, in which case I'm basically thinking unit, integration, e2e.

"If you want to know if your utility classes and functions are sane, unit testing is far better bang for your buck than trying to figure out whether they're being adequately exercised in your service tests."

This is actually where doctests work pretty well as they both document and test.

"If you're trying to figure out which part of a complicated system broke, having unit tests that break on the specific module, or class, or method can be quite helpful."

I don't find tracking down bugs with a repeatable test case to be much of a problem (events in live systems are a different story). It becomes even less of a problem if you sprinkle some assertions around the code that block off invalid code paths.

"Yes, integration tests can be mocked up to look like real world data, and of course you can even feed them real data. The flip side is that their data requirements can be heavy, and they can be quite cumbersome to set up."

Building mocks in unit tests is usually even more cumbersome and tedious.

For overly large sets of real world data I've had some success taking live database snapshots and cutting out 95% of the data before using the cut down to size dump for testing.