restructured the add to app samples (#698)

add_to_app/plugin/ios_using_plugin/IOSUsingPluginUITests/IOSUsingPluginUITests.swift

@@ -0,0 +1,30 @@
+// Copyright 2019 The Flutter team. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import XCTest
+
+class IOSUsingPluginUITests: XCTestCase {
+
+    override func setUp() {
+        // Put setup code here. This method is called before the invocation of each test method in the class.
+
+        // In UI tests it is usually best to stop immediately when a failure occurs.
+        continueAfterFailure = false
+
+        // UI tests must launch the application that they test. Doing this in setup will make sure it happens for each test method.
+        XCUIApplication().launch()
+
+        // In UI tests it’s important to set the initial state - such as interface orientation - required for your tests before they run. The setUp method is a good place to do this.
+    }
+
+    override func tearDown() {
+        // Put teardown code here. This method is called after the invocation of each test method in the class.
+    }
+
+    func testExample() {
+        // Use recording to get started writing UI tests.
+        // Use XCTAssert and related functions to verify your tests produce the correct results.
+    }
+
+}