StackOverflowError When Mocking/Stubbing an ArrayList with MockFor or StubFor

[Ivan Krizsan]

Hi!
When trying to write the following test using MockFor or StubFor to mock/stub an ArrayList, the test fails with a StackOverflowError. The console output is just one single line: "Entering insertItemIntoList: 0"
However, when replacing the ArrayList type with Vector or LinkedList, everything works as it should.
Anyone has any idea why this happens?
Thanks in advance!

import groovy.mock.interceptor.*;
import groovy.util.GroovyTestCase;
import java.util.List

class TestWithMockFor extends GroovyTestCase
{
    void testInserting()
    {
        def theMock = new MockFor(ArrayList)
        theMock.demand.add(4..4) { true }
        
        theMock.use
        {
            def theOUT = new ListUser()
            4.times
            {
               theOUT.insertItemIntoList(it)
            }
        }
    }
}

class ListUser
{
    private List list
    
    ListUser()
    {
        list = new ArrayList()
    }
    
    def insertItemIntoList(def inItem)
    {
        println "Entering insertItemIntoList: $inItem"
        list.add(inItem)
        println "Exiting insertItemIntoList: $inItem"
    }
}