printing SendTxReturnCode in logs will be more readable (#99)

* printing SendTxReturnCode in logs will be more readable

* test improvement for readability

Author: fernandezlautaro

multinode/models.go

@@ -29,6 +29,10 @@ var sendTxSevereErrors = []SendTxReturnCode{Fatal, Underpriced, Unsupported, Exc
 // sendTxSuccessfulCodes - error codes which signal that transaction was accepted by the node
 var sendTxSuccessfulCodes = []SendTxReturnCode{Successful, TransactionAlreadyKnown}
 
+func (c SendTxReturnCode) MarshalText() ([]byte, error) {
+	return []byte(c.String()), nil
+}
+
 func (c SendTxReturnCode) String() string {
 	switch c {
 	case Successful:

multinode/transaction_sender_test.go

@@ -2,6 +2,7 @@ package multinode
 
 import (
 	"context"
+	"encoding/json"
 	"fmt"
 	"testing"
 
@@ -425,3 +426,60 @@ func TestTransactionSender_SendTransaction_aggregateTxResults(t *testing.T) {
 func newSendTxResult(err error) sendTxResult[any] {
 	return sendTxResult[any]{error: err}
 }
+
+func TestLoggableSendTxResults(t *testing.T) {
+	t.Parallel()
+
+	// Input reconstructed from an observed production invariant violation log:
+	// 1 node returned Successful (code 1), 2 nodes returned Unknown (code 5)
+	// with "RPC call failed: TX_REPLAY_ATTACK", triggering "got success and severe error".
+	replayAttackErr := errors.New("RPC call failed: TX_REPLAY_ATTACK")
+	input := sendTxResults[any]{
+		Successful: {
+			{res: nil, code: Successful, error: nil},
+		},
+		Unknown: {
+			{res: nil, code: Unknown, error: replayAttackErr},
+			{res: nil, code: Unknown, error: replayAttackErr},
+		},
+	}
+
+	got := loggableSendTxResults(input)
+
+	require.Equal(t, map[SendTxReturnCode][]map[string]any{
+		Successful: {
+			{"res": nil, "code": Successful, "error": ""},
+		},
+		Unknown: {
+			{"res": nil, "code": Unknown, "error": "RPC call failed: TX_REPLAY_ATTACK"},
+			{"res": nil, "code": Unknown, "error": "RPC call failed: TX_REPLAY_ATTACK"},
+		},
+	}, got)
+
+	b, err := json.Marshal(got)
+	require.NoError(t, err)
+	require.JSONEq(t,
+		`{
+   "Successful":[
+      {
+         "code":"Successful",
+         "error":"",
+         "res":null
+      }
+   ],
+   "Unknown":[
+      {
+         "code":"Unknown",
+         "error":"RPC call failed: TX_REPLAY_ATTACK",
+         "res":null
+      },
+      {
+         "code":"Unknown",
+         "error":"RPC call failed: TX_REPLAY_ATTACK",
+         "res":null
+      }
+   ]
+}`,
+		string(b),
+	)
+}