Add tests for SendError's enhanced status and error codes

Implemented new unit tests for SendError to validate the enhanced status code and error codes in various scenarios, including nil SendError cases, errors with no enhanced status code, and errors with both permanent and temporary error codes. This ensures the correctness of the error handling behavior across different conditions.

senderror_test.go

@@ -218,6 +218,78 @@ func TestSendError_Msg(t *testing.T) {
 	})
 }
 
+func TestSendError_EnhancedStatusCode(t *testing.T) {
+	t.Run("SendError with no enhanced status code", func(t *testing.T) {
+		err := &SendError{
+			errlist: []error{ErrNoRcptAddresses},
+			rcpt:    []string{"<toni.tester@domain.tld>", "<tina.tester@domain.tld>"},
+			Reason:  ErrAmbiguous,
+		}
+		if err.EnhancedStatusCode() != "" {
+			t.Errorf("expected empty enhanced status code, got: %s", err.EnhancedStatusCode())
+		}
+	})
+	t.Run("SendError with enhanced status code", func(t *testing.T) {
+		err := &SendError{
+			errlist:            []error{ErrNoRcptAddresses},
+			rcpt:               []string{"<toni.tester@domain.tld>", "<tina.tester@domain.tld>"},
+			Reason:             ErrAmbiguous,
+			enhancedStatusCode: "5.7.1",
+		}
+		if err.EnhancedStatusCode() != "5.7.1" {
+			t.Errorf("expected enhanced status code: %s, got: %s", "5.7.1", err.EnhancedStatusCode())
+		}
+	})
+	t.Run("enhanced status code on nil error should return empty string", func(t *testing.T) {
+		var err *SendError
+		if err.EnhancedStatusCode() != "" {
+			t.Error("expected empty enhanced status code on nil-senderror")
+		}
+	})
+}
+
+func TestSendError_ErrorCode(t *testing.T) {
+	t.Run("ErrorCode with a go-mail error should return 0", func(t *testing.T) {
+		err := &SendError{
+			errlist: []error{ErrNoRcptAddresses},
+			rcpt:    []string{"<toni.tester@domain.tld>", "<tina.tester@domain.tld>"},
+			Reason:  ErrAmbiguous,
+			errcode: getErrorCode(ErrNoRcptAddresses),
+		}
+		if err.ErrorCode() != 0 {
+			t.Errorf("expected error code: %d, got: %d", 0, err.ErrorCode())
+		}
+	})
+	t.Run("SendError with permanent error", func(t *testing.T) {
+		err := &SendError{
+			errlist: []error{ErrNoRcptAddresses},
+			rcpt:    []string{"<toni.tester@domain.tld>", "<tina.tester@domain.tld>"},
+			Reason:  ErrAmbiguous,
+			errcode: getErrorCode(errors.New("535 5.7.8 Error: authentication failed")),
+		}
+		if err.ErrorCode() != 535 {
+			t.Errorf("expected error code: %d, got: %d", 535, err.ErrorCode())
+		}
+	})
+	t.Run("SendError with temporary error", func(t *testing.T) {
+		err := &SendError{
+			errlist: []error{ErrNoRcptAddresses},
+			rcpt:    []string{"<toni.tester@domain.tld>", "<tina.tester@domain.tld>"},
+			Reason:  ErrAmbiguous,
+			errcode: getErrorCode(errors.New("441 4.1.0 Server currently unavailable")),
+		}
+		if err.ErrorCode() != 441 {
+			t.Errorf("expected error code: %d, got: %d", 441, err.ErrorCode())
+		}
+	})
+	t.Run("error code on nil error should return 0", func(t *testing.T) {
+		var err *SendError
+		if err.ErrorCode() != 0 {
+			t.Error("expected 0 error code on nil-senderror")
+		}
+	})
+}
+
 // returnSendError is a helper method to retunr a SendError with a specific reason
 func returnSendError(r SendErrReason, t bool) error {
 	message := NewMsg()