multi: Add tests to psbt and normal open channel flow.

Itests were added to the normal channel funding flow and the psbt
funding flow using unstable (unconfirmed sweeper inputs).

lntest/harness.go

@@ -1205,6 +1205,7 @@ func (h *HarnessTest) OpenChannelAssertErr(srcNode, destNode *node.HarnessNode,
 
 	// Receive an error to be sent from the stream.
 	_, err := h.receiveOpenChannelUpdate(respStream)
+	require.NotNil(h, err, "expected channel opening to fail")
 
 	// Use string comparison here as we haven't codified all the RPC errors
 	// yet.

lntest/rpc/wallet_kit.go

@@ -68,6 +68,16 @@ func (h *HarnessRPC) FundPsbt(
 	return resp
 }
 
+// FundPsbtAssertErr makes a RPC call to the node's FundPsbt and asserts an
+// error is returned.
+func (h *HarnessRPC) FundPsbtAssertErr(req *walletrpc.FundPsbtRequest) {
+	ctxt, cancel := context.WithTimeout(h.runCtx, DefaultTimeout)
+	defer cancel()
+
+	_, err := h.WalletKit.FundPsbt(ctxt, req)
+	require.Error(h, err, "expected error returned")
+}
+
 // FinalizePsbt makes a RPC call to node's FinalizePsbt and asserts.
 func (h *HarnessRPC) FinalizePsbt(
 	req *walletrpc.FinalizePsbtRequest) *walletrpc.FinalizePsbtResponse {