Reported here: https://github.com/bitcoin/bitcoin/pull/10244#issuecomment-378035305

Travis log here: https://travis-ci.org/bitcoin/bitcoin/jobs/361243719#L2810

Note the JSON exception:

```
test_framework.authproxy.JSONRPCException: The mempool was not loaded yet (-1) 
```

That exception was introduced here: https://github.com/bitcoin/bitcoin/commit/cb1e319fe9e198c9c5cf5236fe9af5a3d748b9e8#diff-a0c8f511d90e83aa9b5857e819ced344R1617

cc @jtimon 
}
}
static UniValue getmempooldescendants(const JSONRPCRequest& request)
{
    if (request.fHelp || request.params.size() < 1 || request.params.size() > 2) {
        throw std::runtime_error(
            RPCHelpMan{"getmempooldescendants",
                "\nIf txid is in the mempool, returns all in-mempool descendants.\n",
                {
                    {"txid", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The transaction id (must be in mempool)"},
                    {"verbose", RPCArg::Type::BOOL,  "false", "True for a json object, false for array of transaction ids"},
                },
                {
                    RPCResult{"for verbose = false",
            "[                       (json array of strings)\n"
            "  \"transactionid\"           (string) The transaction id of an in-mempool descendant transaction\n"
            "  ,...\n"
            "]\n"
                    },
                    RPCResult{"for verbose = true",
            "{                           (json object)\n"
            "  \"transactionid\" : {       (json object)\n"
            + EntryDescriptionString()
            + "  }, ...\n"
            "}\n"
                    },
                },
                RPCExamples{
                    HelpExampleCli("getmempooldescendants", "\"mytxid\"")
            + HelpExampleRpc("getmempooldescendants", "\"mytxid\"")