Hi folks. I’m struggling with a mock setup and co...

# mockk

[Larry Garfield]

Hi folks. I’m struggling with a mock setup and could use help from someone who has, you know, used Kotlin, Mockk, or Spring Boot before February when I started. 😬 (Details in 🧵 )

[Larry Garfield]

I’m writing a Kafka consumer, which I now want to test. It’s not particularly complicated; it just calls a service which saves stuff to the database, give or take some munging of the incoming message. I want to test the consumer.

Normally, I’d approach this by saying “this is an integration test, not unit test, so just use the DB and move on with life.” Problem: Because of how our application is set up (split into 8 separate modules, but the DB is controlled and imported by just one of them), I don’t have actual SQL tables available in the test container DB. (Yes, we’re using postgres test containers. Not my decision.) So if I try to run my test, I get an error that the table is missing (true).

[Larry Garfield]

The PE on the team told me to screw it and just mock the DB, even if that makes the test less useful. OK, fine… but how do I mock the DB across the application (which is booting to handle dependencies) rather than just manually for a single service I create in the test itself? It’s the wiring of everything that I’m testing here.

[Larry Garfield]

Duck Duck Go-ing led me to try this (abbreviated):

@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
class ScraperErrorConsumerTest {

    @Autowired
    lateinit var objectMapper: ObjectMapper

    @Autowired
    lateinit var subject: ScraperErrorConsumer

    @MockBean
    lateinit var repository: ScraperRefreshRepository

    @Test
    fun `error calls are saved`() {
        val uuid = UUID.randomUUID()

        val scrape = ScraperRefresh(
            stateCode = "IL",
            entityName = "Me, Inc",
        )
        scrape.id = uuid

        setupRepositoryMock(mutableMapOf(scrape.id to scrape))

        repository.save(scrape)

        val message = ScraperErrorMessage(
            id = uuid,
            errorType = "Bad",
            title = "Bad",
            request = EntityRefreshEvent(uuid),
        )

        val ack = mockAcknowledgement()

// The actual thing being tested.        subject.consume(objectMapper.writeValueAsString(message), ack)

        val record = repository.findById(uuid)

        // Assertions here
    }

    private fun mockAcknowledgement() = object : Acknowledgment {
        var called = false
        override fun acknowledge() {
            called = true
        }
    }

    private fun setupRepositoryMock(records: MutableMap<UUID, ScraperRefresh>) {
        repository = mockk<ScraperRefreshRepository>()
        every { repository.save(any<ScraperRefresh>()) } answers {
            val updated = it.invocation.args[0] as ScraperRefresh
            records[updated.id] = updated
            updated
        }
        every { repository.findById(any<UUID>()) } answers {
            val uuid = it.invocation.args[0] as UUID
            Optional.ofNullable(records[uuid])
        }
    }
}

The problem is, that doesn’t propagate the mock through to the underlying service that is held by subject. So it saves to I’m not sure where (since there shouldn’t be a DB table?), but then the mocked findById() looks at just the mutable map and doesn’t find the updates.

If I don’t re-set the repository mock in the first line of setupRepositoryMock(), I get an error

Failed matching mocking signature for

left matchers: [any()]

So… I’m confused here. All I can think of is to abandon and just have a pure unit test, but that doesn’t actually buy me anything. I already have tests for the service class so I know it’s covered. It’s specifically the limited logic in the consumer and the wiring in Spring that I want to test, but I cannot for the life of me see how.

[Larry Garfield]

Any suggestions?

[Endre Deak]

Honestly I’d stick to the mock db approach. With flyway you can set up the schema for your test container. Would that work?

[Larry Garfield]

We’re already using flyway, but the SQL files are all in one of the other modules at the moment, so I don’t know how to even get to them. The PE said we should probably move them at some point, but that hasn’t happened.

[Larry Garfield]

(Stick to mock db, meaning drop mockk and use a real DB for this test?)

[Endre Deak]

Yes. Alternatively you can implement a mock repo which saves to some in-memory thing? So you don’t have to mockk

[Larry Garfield]

Um, maybe? I still barely comprehend JPA… 😬

[Larry Garfield]

(I’ve been developing for 25 years, but anything JVM is new to me this year.)

[Endre Deak]

You don’t need JPA. The mock repo would just save to a map or a list

[Larry Garfield]

Right, but I need to conform to the interface for it.

[Endre Deak]

Yes

[Larry Garfield]

Oh! Another Staff just suggested I use a TestConfiguration class to blast the repository from orbit… and that seems to work! (Still using mockk for now.)

[Larry Garfield]

Trying to replace it with a manual class. So far, not so good. 😕

[Jacob]

Did you mean to use @mockkbean? @mockbean is only for mockito

[Larry Garfield]

Well that could be a problem…