***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:
    virtual ~RPCTimerInterface() {}
    
    virtual const char *Name() = 0;
    /** Factory function for timers.
     * RPC will call the function to create a timer that will call func in *millis* milliseconds.
     * @note As the RPC mechanism is backend-neutral, it can use different implementations of timers.
     * This is needed to cope with the case in which there is no HTTP server, but
     * only GUI RPC console, and to break the dependency of pcserver on httprpc.
     */
    virtual RPCTimerBase* NewTimer(std::function<void(void)>& func, int64_t millis) = 0;
};
void RPCSetTimerInterface(RPCTimerInterface *iface);
void RPCSetTimerInterfaceIfUnset(RPCTimerInterface *iface);
void RPCUnsetTimerInterface(RPCTimerInterface *iface);
/**
 * Run func nSeconds from now.
 * Overrides previous timer <name> (if any).
 */
void RPCRunLater(const std::string& name, std::function<void(void)> func, int64_t nSeconds);
typedef UniValue(*rpcfn_type)(const JSONRPCRequest& jsonRequest);
class CRPCCommand