***UPDATE:***

Turns out the issue was caused not by testnet, but by having 2 wallets @ryanofsky found out !

----------

Step to reproduce:

This work on regtest just fine:
```
bitcoind -wallet=test -regtest -rpcpassword=abc -rpcuser=abc
```

Try to make a batch RPC request to /wallet/test:

```
[{"jsonrpc":"1.0","id":1,"method":"getbalance","params":["*"]}]
```
You get the expected result.

However; same things with testnet:
```
bitcoind -wallet=test -testnet -rpcpassword=abc -rpcuser=abc
```

Result:

"Wallet file not specified (must request wallet RPC through /wallet/<filename> uri-path)."

This problem is limited to batched RPC request on testnet as just making the exact same request without the '[' and ']' works fine. It works also fine on regtest, which is crazy. I will look into later.
{
public:
    HTTPRPCTimer(struct event_base* eventBase, std::function<void(void)>& func, int64_t millis) :
        ev(eventBase, false, func)
    {
        struct timeval tv;
        tv.tv_sec = millis/1000;
        tv.tv_usec = (millis%1000)*1000;
        ev.trigger(&tv);
    }
private:
    HTTPEvent ev;
};
class HTTPRPCTimerInterface : public RPCTimerInterface
{
public:
    explicit HTTPRPCTimerInterface(struct event_base* _base) : base(_base)