Simba Testing

Testing Simba-Based Code

Test Strategy Overview

Simba testing has three layers:

1. Unit tests — mock the MutexContendServiceFactory, test your business logic in isolation
2. TCK (Technology Compatibility Kit) — extend MutexContendServiceSpec to verify a backend implementation
3. Integration tests — run against a real backend (Redis, MySQL, Zookeeper)

Choose the simplest layer that gives confidence. Most application code only needs unit tests with mocks. Backend implementors need TCK + integration tests.

Before writing a test, decide:

• Application behavior: mock MutexContendServiceFactory, capture the contender, and pass ownership changes to notifyOwner.
• Backend implementation: extend MutexContendServiceSpec and run against the real backend.
• Scheduler behavior: verify leadership gating separately from the business logic in work().

Unit Tests with MockK

For application code that injects MutexContendServiceFactory, call the component under test and mock only the factory seam:

import io.mockk.every
import io.mockk.mockk
import io.mockk.verify
import me.ahoo.simba.core.MutexContendService
import me.ahoo.simba.core.MutexContendServiceFactory
import me.ahoo.simba.core.MutexContender
import me.ahoo.simba.core.MutexOwner
import me.ahoo.simba.core.MutexState

class MyComponentTest {
    private val mockFactory = mockk<MutexContendServiceFactory>()
    private val mockService = mockk<MutexContendService>(relaxed = true)

    @BeforeEach
    fun setup() {
        every { mockFactory.createMutexContendService(any()) } returns mockService
    }

    @Test
    fun `should start contend service`() {
        val myComponent = MyComponent(mockFactory)
        myComponent.start()

        verify(exactly = 1) { mockService.start() }
    }
}

Simulating Leadership Changes

To test code that reacts to onAcquired/onReleased, capture the contender and pass states through its real notifyOwner dispatch:

@Test
fun `should react to leadership change`() {
    val contenderSlot = slot<MutexContender>()
    every { mockFactory.createMutexContendService(capture(contenderSlot)) } returns mockService

    // Create your service/component that uses Simba
    val myComponent = MyComponent(mockFactory)
    myComponent.start()

    // Simulate acquiring leadership
    val contender = contenderSlot.captured
    val owner = MutexOwner(contender.contenderId)
    contender.notifyOwner(MutexState(MutexOwner.NONE, owner))

    // Assert your component's behavior
    myComponent.isLeader.assert().isTrue()

    // Simulate losing leadership
    contender.notifyOwner(MutexState(owner, MutexOwner.NONE))

    myComponent.isLeader.assert().isFalse()
}

SimbaLocker Unit Tests

Mock the factory and verify the locker lifecycle:

import me.ahoo.simba.locker.SimbaLocker

@Test
fun `locker should stop running service on close`() {
    val mockService = mockk<MutexContendService>(relaxed = true)
    every { mockFactory.createMutexContendService(any()) } returns mockService
    every { mockService.running } returns true

    val locker = SimbaLocker("test-lock", mockFactory)
    locker.close()

    verify { mockService.stop() }
}

Stub running as true because close() calls stop() only for an active contend service.

TCK — Extending MutexContendServiceSpec

When implementing a new Simba backend, extend the TCK to verify correctness:

import me.ahoo.simba.test.MutexContendServiceSpec

class MyBackendMutexContendServiceTest : MutexContendServiceSpec() {
    override val mutexContendServiceFactory: MutexContendServiceFactory =
        MyBackendMutexContendServiceFactory(/* dependencies */)
}

This gives you five standard tests:

1. start() — acquire, verify owner, stop, verify released
2. restart() — stop and restart, verify full lifecycle repeats
3. guard() — acquire, wait 3s, verify owner hasn't changed (TTL renewal works)
4. multiContend() — 10 contenders compete, exactly one owner at any time
5. schedule() — AbstractScheduler lifecycle, work executes on leader

Backend-Specific Test Requirements

Do not silently add Testcontainers to this repository's tests. If CI isolation is required, add the dependency and Gradle wiring intentionally, then update the backend setup code and this skill together.

AbstractScheduler Tests

Test that scheduled work runs only on the leader:

import io.mockk.capture
import io.mockk.every
import io.mockk.mockk
import io.mockk.slot
import me.ahoo.simba.core.MutexContendService
import me.ahoo.simba.core.MutexContendServiceFactory
import me.ahoo.simba.core.MutexContender
import me.ahoo.simba.core.MutexOwner
import me.ahoo.simba.core.MutexState
import me.ahoo.simba.schedule.AbstractScheduler
import me.ahoo.simba.schedule.ScheduleConfig
import me.ahoo.test.asserts.assert
import org.junit.jupiter.api.Test
import java.time.Duration
import java.util.concurrent.CountDownLatch
import java.util.concurrent.TimeUnit
import java.util.concurrent.atomic.AtomicBoolean

@Test
fun `scheduler should run work only when leader`() {
    val contenderSlot = slot<MutexContender>()
    val mockService = mockk<MutexContendService>(relaxed = true)
    val mockFactory = mockk<MutexContendServiceFactory>()
    every { mockFactory.createMutexContendService(capture(contenderSlot)) } returns mockService
    val leader = AtomicBoolean(false)
    val leaderWork = CountDownLatch(1)
    val outsideLeadershipWork = CountDownLatch(1)
    val scheduler = object : AbstractScheduler("test-scheduler", mockFactory) {
        override val config = ScheduleConfig.delay(Duration.ZERO, Duration.ofMillis(100))
        override val worker = "test"
        override fun work() {
            if (leader.get()) leaderWork.countDown() else outsideLeadershipWork.countDown()
        }
    }

    scheduler.start()
    val contender = contenderSlot.captured
    val owner = MutexOwner(contender.contenderId)
    try {
        outsideLeadershipWork.await(200, TimeUnit.MILLISECONDS).assert().isFalse()
        leader.set(true)
        contender.notifyOwner(MutexState(MutexOwner.NONE, owner))
        leaderWork.await(5, TimeUnit.SECONDS).assert().isTrue()
        contender.notifyOwner(MutexState(owner, MutexOwner.NONE))
        leader.set(false)
        outsideLeadershipWork.await(200, TimeUnit.MILLISECONDS).assert().isFalse()
    } finally {
        if (leader.getAndSet(false)) {
            contender.notifyOwner(MutexState(owner, MutexOwner.NONE))
        }
        scheduler.stop()
    }
}

Assertion Style

Use fluent-assert for new Kotlin assertions:

import me.ahoo.test.asserts.assert

value.assert().isEqualTo(expected)
collection.assert().hasSize(3)
bool.assert().isTrue()

Do not churn existing Hamcrest/AssertJ assertions solely for style. When adding or touching assertions, prefer .assert() and keep the local test readable.

Common Test Pitfalls

1. Timing-dependent tests: Distributed lock tests are inherently timing-sensitive. Use generous timeouts (5-30s) and prefer CountDownLatch / CompletableFuture over new Thread.sleep calls.
2. Shared mutex names: Each test should use a unique mutex name to avoid cross-test interference. Use "test-mutex-${UUID.randomUUID()}".
3. Resource cleanup: Always stop/close services in @AfterEach to avoid leaked threads and held locks.
4. Mocking MutexContendService vs MutexContendServiceFactory: Mock the factory (the DI seam), not the service directly. The factory is what application code injects.
5. Testing AbstractScheduler without Simba: If you only need to test the work() method, call it directly. The scheduler pattern is about leadership gating, not the work itself.