feat : add example project for testing plugin.

example/test/widget_test.dart

@@ -0,0 +1,25 @@
+// This is a basic Flutter widget test.
+// To perform an interaction with a widget in your test, use the WidgetTester utility that Flutter
+// provides. For example, you can send tap and scroll gestures. You can also use WidgetTester to
+// find child widgets in the widget tree, read text, and verify that the values of widget properties
+// are correct.
+
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import 'package:hello_example/main.dart';
+
+void main() {
+  testWidgets('Verify Platform version', (WidgetTester tester) async {
+    // Build our app and trigger a frame.
+    await tester.pumpWidget(new MyApp());
+
+    // Verify that platform version is retrieved.
+    expect(
+        find.byWidgetPredicate(
+          (Widget widget) =>
+              widget is Text && widget.data.startsWith('Running on:'),
+        ),
+        findsOneWidget);
+  });
+}