I kind of suck at boolean algebra, but:
https://github.com/bitcoin/bitcoin/blob/37612099ec7314b15a07d8bac55161ed4e8e7491/src/rpc/rawtransaction.cpp#L1672


Unless I'm mistaken (which is highly likely) the whole thing can't work  (except the edge case where `permitsigdata=true` and you have no sig data) 
{
    if (request.fHelp || request.params.size() < 1 || request.params.size() > 2) {
        throw std::runtime_error(
            
            "testmempoolaccept [\"rawtxs\"] ( allowhighfees )\n"
            "\nReturns if raw transaction (serialized, hex-encoded) would be accepted by mempool.\n"
            "\nThis checks if the transaction violates the consensus or policy rules.\n"
            "\nSee sendrawtransaction call.\n"
            "\nArguments:\n"
            "1. [\"rawtxs\"]       (array, required) An array of hex strings of raw transactions.\n"
            "                                        Length must be one for now.\n"
            "2. allowhighfees    (boolean, optional, default=false) Allow high fees\n"
            "\nResult:\n"
            "[                   (array) The result of the mempool acceptance test for each raw transaction in the input array.\n"
            "                            Length is exactly one for now.\n"
            " {\n"
            "  \"txid\"           (string) The transaction hash in hex\n"
            "  \"allowed\"        (boolean) If the mempool allows this tx to be inserted\n"
            "  \"reject-reason\"  (string) Rejection string (only present when 'allowed' is false)\n"
            " }\n"
            "]\n"
            "\nExamples:\n"
            "\nCreate a transaction\n"
            + HelpExampleCli("createrawtransaction", "\"[{\\\"txid\\\" : \\\"mytxid\\\",\\\"vout\\\":0}]\" \"{\\\"myaddress\\\":0.01}\"") +
            "Sign the transaction, and get back the hex\n"
            + HelpExampleCli("signrawtransactionwithwallet", "\"myhex\"") +
            "\nTest acceptance of the transaction (signed hex)\n"
            + HelpExampleCli("testmempoolaccept", "\"signedhex\"") +
            "\nAs a json rpc call\n"