test(mail): assert typed ExitError in TestValidateNoSignatureConflict

Use errors.As + *output.ExitError to assert exit code ExitValidation(2)
and detail type "validation", consistent with mail_confirm_send_scope_test.go.

Change-Type: ci-fix

Author: xzcong0820

shortcuts/mail/signature_compose_test.go

@@ -4,17 +4,26 @@
 package mail
 
 import (
+	"errors"
 	"testing"
+
+	"github.com/larksuite/cli/internal/output"
 )
 
 func TestValidateNoSignatureConflictTypedError(t *testing.T) {
 	err := validateNoSignatureConflict(true, "sig_123")
 	if err == nil {
 		t.Fatal("expected error, got nil")
 	}
-	// output.ErrValidation returns *output.ExitError (exit code 2).
-	if err.Error() == "" {
-		t.Fatalf("expected non-empty error message, got %T (%v)", err, err)
+	var exitErr *output.ExitError
+	if !errors.As(err, &exitErr) {
+		t.Fatalf("expected *output.ExitError, got %T: %v", err, err)
+	}
+	if exitErr.Code != output.ExitValidation {
+		t.Errorf("expected exit code %d (ExitValidation), got %d", output.ExitValidation, exitErr.Code)
+	}
+	if exitErr.Detail == nil || exitErr.Detail.Type != "validation" {
+		t.Errorf("expected detail type validation, got %+v", exitErr.Detail)
 	}
 }