Broken spying on functions

[GFriedrich]

Expected Behavior

Calling a line like val test: (Int) -> Unit = spyk({}) shouldn't fail.

Current Behavior

Running this line fails with:

This class is an internal synthetic class generated by the Kotlin compiler, such as an anonymous class for a lambda, a SAM wrapper, a callable reference, etc. It's not a Kotlin class or interface, so the reflection library has no idea what declarations it has.

Failure Information (for bugs)

This got likely broken because of the ProxyMaker deduplication of #1024

Steps to Reproduce

1. Add a line like val test: (Int) -> Unit = spyk({}) to a unit test
2. Run the test

Context

• MockK version: 1.13.4
• Kotlin version: 1.6
• JDK version: 17
• Type of test: unit test

[SimonMarquis]

I can confirm this worked on the previous version 1.13.3.
The current workaround for us has been to do the following:

val lambda = spyk<() -> Unit>()
// or
val lambda: () -> Unit = spyk()

[sampengilly]

For non-trivial spy'd lambdas such as ones that need to return a value, the following seems to be necessary:

val lambda: (Int, String) -> Boolean = spyk {
    every { this@spyk.invoke(any(), any()) } answers { ... }
}

EDIT: Or moving the every out of the spyk {} block

[JohannesTeichert]

For non-trivial spy'd lambdas such as ones that need to return a value, the following seems to be necessary:

val lambda: (Int, String) -> Boolean = spyk {
    every { this@spyk.invoke(any(), any()) } answers { ... }
}

EDIT: Or moving the every out of the spyk {} block

Thanks for this answer, helped me find a solution for my very similar problem.

I had to change me spyk instantiation from this:

val userListObserver: Observer<List<User>> = spyk(Observer { })

to this:

val userListObserver: Observer<List<User>> = spyk { Observer<List<User>>{  } }

what I still get which is new since the update is this slf4j logger provider warning:

SLF4J: No SLF4J providers were found.
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See https://www.slf4j.org/codes.html#noProviders for further details.

[krissrex]

what I still get which is new since the update is this slf4j logger provider warning:

SLF4J: No SLF4J providers were found.
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See https://www.slf4j.org/codes.html#noProviders for further details.

SLF4J version 2.0.5 is a dependency of mockk.

This specific issue happens when your slf4j version is updated, but your logback version is old.
They had a breaking update recently.
Try:

<slf4j.version>2.0.6</slf4j.version>
<logback.version>1.4.5</logback.version>

[krissrex]

I have the same problem when spying on fun interface implementations:

Fails:

spyk(
  MyFunInterface { 1 + 2 }
)

Works:

spyk(
  object : MyFunInterface {
    override fun doThing(): Int = 1 + 2
  }
)

[heli-os]

I'm experiencing the same problem in 1.13.4. I downgraded to 1.13.3, and it is being used temporarily.

ex)

interface Logger {

    fun interface Factory {
        fun getLogger(name: String): Logger

        fun getLogger(clazz: Class<*>): Logger = getLogger(clazz.name)
    }
}

// Error Occurred
val sut = spyk(Logger.Factory { NoOpLogger })
sut.getLogger(LoggerTest::class.java)
verify(exactly = 1) {
    sut.getLogger(any<String>())
}

[carterhudson]

This is still a problem in 1.13.7.
I would use 1.13.3, but it has this issue.
:(