When trying to mock a WeakReference, a StackOverflowError occurs.

[IosephKnecht]

Hi, I ran into the problem of hanging tests when they have mock WeakReference.
The test code looks something like this:

class FooTest {

    @Test
    fun test() {
        val weakReference = Mockito.mock(WeakReference::class.java) as WeakReference<Bar>
        val bar = Mockito.mock(Bar::class.java)

        Mockito.doReturn(bar).`when`(weakReference).get()

        val foo = Foo(weakReference)
        val consumedBar = foo.get()

        Mockito.verify(foo.get())
        Assertions.assertEquals(consumedBar, bar)
    }
}

Is there any way around this, or is it impossible?

Stacktrace

Exception: java.lang.StackOverflowError thrown from the UncaughtExceptionHandler in thread "/127.0.0.1:52766 to /127.0.0.1:52765 workers Thread 2"
Exception: java.lang.StackOverflowError thrown from the UncaughtExceptionHandler in thread "Test worker"
Exception: java.lang.StackOverflowError thrown from the UncaughtExceptionHandler in thread "process reaper"
Exception: java.lang.StackOverflowError thrown from the UncaughtExceptionHandler in thread "/127.0.0.1:52766 to /127.0.0.1:52765 workers Thread 4"
Exception: java.lang.StackOverflowError thrown from the UncaughtExceptionHandler in thread "process reaper"
Exception: java.lang.StackOverflowError thrown from the UncaughtExceptionHandler in thread "/127.0.0.1:52766 to /127.0.0.1:52765 workers Thread 5"
Exception: java.lang.StackOverflowError thrown from the UncaughtExceptionHandler in thread "process reaper"
Exception: java.lang.StackOverflowError thrown from the UncaughtExceptionHandler in thread "/127.0.0.1:52766 to /127.0.0.1:52765 workers Thread 6"
Exception: java.lang.StackOverflowError thrown from the UncaughtExceptionHandler in thread "process reaper"
Exception: java.lang.StackOverflowError thrown from the UncaughtExceptionHandler in thread "/127.0.0.1:52766 to /127.0.0.1:52765 workers Thread 7"
Exception: java.lang.StackOverflowError thrown from the UncaughtExceptionHandler in thread "process reaper"
Exception: java.lang.StackOverflowError thrown from the UncaughtExceptionHandler in thread "/127.0.0.1:52766 to /127.0.0.1:52765 workers Thread 8"

Versions

Mockito core version = 3.12.4
Mockito inline version = 3.12.4
Junit5 version = 1.7.20
OS Version = macOS:12.5.1:21G83
JDK version = openjdk 15.0.2 2021-01-19
OpenJDK Runtime Environment Corretto-15.0.2.7.1 (build 15.0.2+7)
OpenJDK 64-Bit Server VM Corretto-15.0.2.7.1 (build 15.0.2+7, mixed mode, sharing)

Notes

The error cannot be reproduced without connecting mockito-inline, perhaps the problem is org.mockito.internal.creation.bytebuddy.InlineByteBuddyMockMaker.

Full sample

[TimvdLippe]

Unfortunately, WeakReference is one of the classes that Mockito relies on internally for its behavior. Stubbing WeakReference will therefore lead to undefined behavior. Additionally, it is advised not to mock classes you don't own: https://github.com/mockito/mockito/wiki/How-to-write-good-tests#dont-mock-a-type-you-dont-own We are working on improving the user experience by working on a DoNotMock feature to avoid mocking classes/methods that are known to crash Mockito internals (#1833). Therefore, I am closing this as "Infeasible". Apologies for the uninformative exception that is thrown.

[IosephKnecht]

@TimvdLippe Thanks for the reply.