Fix error handling to not set errorText if error is set.

Author: dsyrstad

lib/vsc_datetime_field.dart

@@ -269,8 +269,11 @@ class VscDatetimeFieldState extends State<VscDatetimeField> {
       focusNode: _effectiveFocusNode,
       controller: _effectiveController,
       decoration: widget.textFieldConfiguration.decoration.copyWith(
-        errorText: _internalErrorText ??
-            widget.textFieldConfiguration.decoration.errorText,
+        // Only set errorText if there's no error widget already provided
+        errorText: widget.textFieldConfiguration.decoration.error == null
+            ? (_internalErrorText ??
+                widget.textFieldConfiguration.decoration.errorText)
+            : null,
         suffixIcon: Semantics(
           identifier: 'id_datetime_field_suffix_icon',
           child: InkResponse(

test/vsc_datetime_field_error_handling_test.dart

@@ -0,0 +1,86 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:vsc_datetime_field/vsc_datetime_field.dart';
+
+void main() {
+  group('VscDatetimeField error handling', () {
+    testWidgets('handles error widget in decoration without assertion error',
+        (WidgetTester tester) async {
+      // Build a VscDatetimeField with an error widget in the decoration
+      await tester.pumpWidget(
+        MaterialApp(
+          home: Scaffold(
+            body: VscDatetimeField(
+              textFieldConfiguration: const TextFieldConfiguration(
+                decoration: InputDecoration(
+                  labelText: 'Test Field',
+                  // This simulates what UiEditorDatetimeField does
+                  error: Text('External validation error'),
+                  errorMaxLines: 3,
+                ),
+              ),
+            ),
+          ),
+        ),
+      );
+
+      // The widget should build without throwing an assertion error
+      expect(find.byType(VscDatetimeField), findsOneWidget);
+      expect(find.text('External validation error'), findsOneWidget);
+
+      // Now trigger an internal error by typing invalid date
+      await tester.enterText(find.byType(TextField), '5/3/');
+      await tester.pump();
+
+      // Should still show only the external error widget, not internal errorText
+      expect(find.text('External validation error'), findsOneWidget);
+      expect(find.text('Invalid value'), findsNothing);
+    });
+
+    testWidgets('shows internal error when no external error widget exists',
+        (WidgetTester tester) async {
+      await tester.pumpWidget(
+        MaterialApp(
+          home: Scaffold(
+            body: VscDatetimeField(
+              textFieldConfiguration: const TextFieldConfiguration(
+                decoration: InputDecoration(
+                  labelText: 'Test Field',
+                  // No error widget provided
+                ),
+              ),
+            ),
+          ),
+        ),
+      );
+
+      // Enter invalid date
+      await tester.enterText(find.byType(TextField), '5/3/');
+      await tester.pump();
+
+      // Should show the internal error text
+      expect(find.text('Invalid value'), findsOneWidget);
+    });
+
+    testWidgets('respects existing errorText when no internal error',
+        (WidgetTester tester) async {
+      await tester.pumpWidget(
+        MaterialApp(
+          home: Scaffold(
+            body: VscDatetimeField(
+              textFieldConfiguration: const TextFieldConfiguration(
+                decoration: InputDecoration(
+                  labelText: 'Test Field',
+                  errorText: 'Pre-existing error text',
+                ),
+              ),
+            ),
+          ),
+        ),
+      );
+
+      // Should show the pre-existing error text
+      expect(find.text('Pre-existing error text'), findsOneWidget);
+    });
+  });
+}