Let us change the return type of our saveMove method to boolean:

@Test 
public void whenSaveMoveThenReturnTrue() {
  TicTacToeBean bean = new TicTacToeBean(3, 2, 1, 'Y');
  MongoCollection mongoCollection = mock(MongoCollection.class);
  doReturn(mongoCollection).when(collection).getMongoCollection();
  assertTrue(collection.saveMove(bean));
}