Hello @obernardovieira! This is kind of a wild guess, but maybe the problem is that your initialize() function is overloaded and the test doesn't know which one to pick? (Or is picking the wrong one) IE: there is an initialize() in Ownable.sol and there is an initialize() in Whitelist, but maybe the test is calling the Ownable initialize() but not Whitelist? Again, wild guess.
I just wrote up a little mini-tip regarding testing for overloaded functions. I haven't tried it in the context of zos testing yet, but it works for truffle-contract based tests. Maybe have a look?