Added test coverage to FormBuilderRating for a read-only variant.

Author: awhitford

test/fields/form_builder_rating_test.dart

@@ -3,10 +3,11 @@ import 'package:flutter_form_builder/flutter_form_builder.dart';
 import 'form_builder_tester.dart';
 
 void main() {
-  testWidgets('FormBuilderRating -- 3', (WidgetTester tester) async {
+  testWidgets('FormBuilderRating -- enabled', (WidgetTester tester) async {
     const widgetName = 'r1';
     final testWidget = FormBuilderRating(
       name: widgetName,
+      initialValue: 1.0,
     );
     await tester.pumpWidget(buildTestableFieldWidget(testWidget));
 
@@ -17,4 +18,21 @@ void main() {
     expect(formSave(), isTrue);
     expect(formValue(widgetName), equals(3.0));
   });
+
+  testWidgets('FormBuilderRating -- readOnly', (WidgetTester tester) async {
+    const widgetName = 'r2';
+    final testWidget = FormBuilderRating(
+      name: widgetName,
+      initialValue: 2.0,
+      enabled: false,
+    );
+    await tester.pumpWidget(buildTestableFieldWidget(testWidget));
+
+    expect(formSave(), isTrue);
+    expect(formValue(widgetName), equals(2.0));
+    await tester.tap(find.byWidget(testWidget));
+    await tester.pumpAndSettle();
+    expect(formSave(), isTrue);
+    expect(formValue(widgetName), equals(2.0));
+  });
 }