Fix Invariant Violation on context cancelled (#27)

* Relax errors

* Update transaction_sender.go

* Revert errors

* Update node_lifecycle.go

* Update transaction_sender_test.go

* Update transaction_sender_test.go

* Update transaction_sender_test.go

* Update transaction_sender.go

* Close txSender before reading logs

Author: DylanTinianov

multinode/transaction_sender.go

@@ -191,13 +191,9 @@ func (txSender *TransactionSender[TX, RESULT, CHAIN_ID, RPC]) reportSendTxAnomal
 		resultsByCode[txResult.code] = append(resultsByCode[txResult.code], txResult)
 	}
 
-	select {
-	case <-txSender.chStop:
-		// it's ok to receive no results if txSender is closing. Return early to prevent false reporting of invariant violation.
-		if len(resultsByCode) == 0 {
-			return
-		}
-	default:
+	// We can receive no results if context was cancelled too early or txSender is closing.
+	if len(resultsByCode) == 0 {
+		return
 	}
 
 	_, criticalErr := aggregateTxResults(resultsByCode)

multinode/transaction_sender_test.go

@@ -138,6 +138,26 @@ func TestTransactionSender_SendTransaction(t *testing.T) {
 		require.EqualError(t, err, "context canceled")
 	})
 
+	t.Run("Context cancelled while sending results does not cause invariant violation", func(t *testing.T) {
+		requestContext, cancel := context.WithCancel(tests.Context(t))
+		mainNode := newNode(t, nil, func(_ mock.Arguments) {
+			cancel()
+		})
+
+		lggr, observedLogs := logger.TestObserved(t, zap.WarnLevel)
+
+		chainID := RandomID()
+		mn := sendTxMultiNode{NewMultiNode[ID, TestSendTxRPCClient](
+			lggr, NodeSelectionModeRoundRobin, 0, []Node[ID, TestSendTxRPCClient]{mainNode}, nil, chainID, "chainFamily", 0)}
+		txSender := NewTransactionSender[any, any, ID, TestSendTxRPCClient](lggr, chainID, mn.chainFamily, mn.MultiNode, func(err error) SendTxReturnCode { return 0 }, tests.TestInterval)
+		require.NoError(t, txSender.Start(tests.Context(t)))
+
+		_, _, err := txSender.SendTransaction(requestContext, nil)
+		require.EqualError(t, err, "context canceled")
+		require.NoError(t, txSender.Close())
+		require.Empty(t, observedLogs.FilterMessage("observed invariant violation on SendTransaction").Len())
+	})
+
 	t.Run("Soft timeout stops results collection", func(t *testing.T) {
 		chainID := RandomID()
 		expectedError := errors.New("transaction failed")