    manager.functions.addToken(vault.address, dai.address).transact()
    manager.functions.addToken(vault.address, dai.address).transact()
require(vaults[_token] == address(0));
bool notFound = True;
for(uint256 i; i < tokens[_vault].length; i++) {
    if (tokens[_vault] == _token) {
        notFound = False;
    }
}
require(notFound, "duplicate token");
