Added unit test for FormBuilderRating.

Author: awhitford

test/fields/form_builder_rating_test.dart

@@ -0,0 +1,20 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter_form_builder/flutter_form_builder.dart';
+import 'form_builder_tester.dart';
+
+void main() {
+  testWidgets('FormBuilderRating -- 3', (WidgetTester tester) async {
+    const widgetName = 'r1';
+    final testWidget = FormBuilderRating(
+      name: widgetName,
+    );
+    await tester.pumpWidget(buildTestableFieldWidget(testWidget));
+
+    expect(formSave(), isTrue);
+    expect(formValue(widgetName), equals(1.0));
+    await tester.tap(find.byWidget(testWidget));
+    await tester.pumpAndSettle();
+    expect(formSave(), isTrue);
+    expect(formValue(widgetName), equals(3.0));
+  });
+}