Mockk: Bug: capture Slots in multiple verifications capture only last value

[tmarsteel]

Expected Behavior & Current Behaviour

Capturing slots work like you'd expect them to, coming from mockito. See this test-case:

open class MockedSubject {
    open fun doSomething(id: String?, data: Any?): String {
        throw IllegalStateException("Not mocked :(")
    }
}

val mock = mockk<MockedSubject>()

every { mock.doSomething("1", "data1") } returns "result1"
every { mock.doSomething("2", "data2") } returns "result2"

mock.doSomething("1", "data1")
mock.doSomething("2", "data2")

val dataSlotId1 = slot<String>()
val dataSlotId2 = slot<String>()

verify (exactly = 1) { mock.doSomething("1", capture(dataSlotId1)) }
verify (exactly = 1) { mock.doSomething("2", capture(dataSlotId2)) }

dataSlotId1.captured shouldBe "data1"
dataSlotId2.captured shouldBe "data2"

This fails because dataSlotId1.captured is "data2"

Steps to Reproduce

I've put all code necessary to reproduce here: https://github.com/tmarsteel/mockk-verify-capture-test

Just run mvn clean test or run the test in your IDE.

Context

See the pom.xml in the repository.

• MockK version: 1.9.3
• OS: Ubuntu 18.04
• Kotlin version: 1.3.41
• JDK version: fails on OpenJDK 1.8.0_222 and 11.0.2 and HotSpot 10.0.2
• JUnit version: fails with 4.12 and Jupiter 5.5.1
• Type of test: unit test

Failure Logs

Stack trace

from the screenshot:

org.opentest4j.AssertionFailedError: expected: "data1" but was: "data2"
Expected :"data1"
Actual   :"data2"
<Click to see difference>


    at com.acme.ExampleTest.test(MockkDebugTest.kt:30)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:532)
    at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:115)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$6(TestMethodTestDescriptor.java:171)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:72)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:167)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:114)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:59)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$4(NodeTestTask.java:108)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:72)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:98)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:74)

[tunovic]

@tmarsteel Maybe not ideal, but have you tried verifyOrder?

verifyOrder {
    mock.doSomething("1", capture(dataSlotId1)) 
    mock.doSomething("2", capture(dataSlotId2))
}

[only-fabione]

Did you try using a list instead of a slot and then capture it?
I did it in this way and it works

val slotIds = mutableListOf<String>()
every { mock.doSomething(capture(slotIds)) } just Runs
val firstSlot = slotIds[0]
val secondSlot = slotIds[1]

[tmarsteel]

@tunovic @only-fabione both work. I don't know how i solved it back then, probably with the list.

[Raibaz]

Sent out #533 to fix this.

The fix is actually suggesting what @only-fabione said earlier, to use a mutableList when capturing the same function arguments more than once.

It should be clearer now why MockK is not behaving as expected when using slots in this case.