Mocking a method inside another method

This is the method i'm testing and i'm using mockito for mocking:

 /**
* Sync get all children under single zk node.
*
* @param zk
*          zookeeper client
* @param node
*          node path
* @return direct children
* @throws InterruptedException
* @throws IOException
*/
public static List<String> getChildrenInSingleNode(final ZooKeeper zk, final String node, long zkOpTimeoutMs)
throws InterruptedException, IOException, KeeperException.NoNodeException {
final GetChildrenCtx ctx = new GetChildrenCtx();
getChildrenInSingleNode(zk, node, new GenericCallback<List<String>>() {
@Override
public void operationComplete(int rc, List<String> ledgers) {
synchronized (ctx) {
if (Code.OK.intValue() == rc) {
ctx.children = ledgers;
}
ctx.rc = rc;
ctx.done = true;
ctx.notifyAll();
}
}
});
synchronized (ctx) {
long startTime = System.currentTimeMillis();
while (!ctx.done) {
try {
ctx.wait(zkOpTimeoutMs > 0 ? zkOpTimeoutMs : 0);
} catch (InterruptedException e) {
ctx.rc = Code.OPERATIONTIMEOUT.intValue();
ctx.done = true;
}
// timeout the process if get-children response not received
// zkOpTimeoutMs.
if (zkOpTimeoutMs > 0 && (System.currentTimeMillis() - startTime) >= zkOpTimeoutMs) {
ctx.rc = Code.OPERATIONTIMEOUT.intValue();
ctx.done = true;
}
}
}
if (Code.NONODE.intValue() == ctx.rc) {
throw new KeeperException.NoNodeException("Got NoNode on call to getChildren on path " + node);
} else if (Code.OK.intValue() != ctx.rc) {
throw new IOException("Error on getting children from node " + node);
}
return ctx.children;
}

And this is my test class:

@RunWith(value= Parameterized.class)
public class ZkUtilsGetChildrenTest  {
private boolean expectedResult;
private ZooKeeper zkc ;
private String path;
private long timeout;
private static List<String> paths = Arrays.asList("/ledgers/000/000/000/001", "/ledgers/000/000/000/002",
"/ledgers/000/000/000/003");
private static List<String> childPaths = Arrays.asList("001", "002", "003");
// ZooKeeper related variables
private static ZooKeeperUtil zkUtil = new ZooKeeperUtil();
@Mock
ZkUtils.GetChildrenCtx mocked = mock(ZkUtils.GetChildrenCtx.class) ;
@BeforeClass
public static  void setUp() throws Exception {
zkUtil.startCluster();
ZooKeeper initializerZkc = new ZooKeeper(zkUtil.getZooKeeperConnectString(), 10000, null);
for (String path : paths ){
ZkUtils.createFullPathOptimistic(initializerZkc, path, "data".getBytes() , ZooDefs.Ids.OPEN_ACL_UNSAFE ,
CreateMode.CONTAINER);
}
}
@AfterClass
public static void tearDown() throws Exception {
zkUtil.killCluster();
}
@Parameterized.Parameters
public static Collection<Object[]> getTestParameters() throws IOException {
return Arrays.asList(new Object[][]{
{false , "null" , "/ledgers/000/000/000/004" , 0},
{true , "new" , "/ledgers/000/000/000" , 1000 },
{false , "wrong" , "/ledgers/000/000/000/00b" , -1},
{false , "new" , "/ledgers/000/000/00b" , 0 },//aggiunto per migliorare statement e branch coverage
{false , "new" , "/ledgers/000/000/003" , 1 },//aggiunto per migliorare statement e branch coverage
{false , "mock" , "/ledgers/000/000" , 1000 },//aggiunto per migliorare statement coverage
});
}
public ZkUtilsGetChildrenTest(boolean expectedResult ,String zkc , String path , long timeout) throws IOException {
if(zkc == "null"){
this.zkc = null;
}else if( zkc == "wrong"){
this.zkc = new ZooKeeper("wrongString", 10000, null);
}else if(zkc == "new"){
this.zkc = new ZooKeeper(zkUtil.getZooKeeperConnectString(), 10000, null);
}else if(zkc == "mock"){
//TODO MOCK THE INNER METHOD
this.zkc = new ZooKeeper(zkUtil.getZooKeeperConnectString(), 10000, null);
when(mocked).thenThrow(new InterruptedException());
}
this.expectedResult = expectedResult;
this.path = path;
this.timeout = timeout;
}
@Test
public void testGetChildrenInSingleNode() {
boolean realResult;
try {
List<String> children = ZkUtils.getChildrenInSingleNode(zkc, path, timeout);
assertThat(children, is(childPaths));
} catch (Exception e) {
realResult = false;
e.printStackTrace();
assertEquals(expectedResult, realResult);
}
}
}

I would like to ask you how can i mock the method ctx.wait(zkOpTimeoutMs > 0 ? zkOpTimeoutMs : 0); so that i can trigger the catch block which follows this statement : if i called this method i would have mocked an istance of this class and call the method on that mock but since is not me who calls this method but it's called by the method under test, how can i properly mock it?

Good day to everyone!

You can use Powermock to mock the creation of new objects if that is something available to you and you cannot or do not want to refactor the existing code. Using Powermock is not without its own downsides, but is a powerful way to gain more granular control over this and other cases (static class/methods and private/protected classes/methods/fields).