add example code to experiment with dart/flutter

ios/RunnerTests/RunnerTests.swift

@@ -0,0 +1,12 @@
+import Flutter
+import UIKit
+import XCTest
+
+class RunnerTests: XCTestCase {
+
+  func testExample() {
+    // If you add code to the Runner application, consider adding tests here.
+    // See https://developer.apple.com/documentation/xctest for more information about using XCTest.
+  }
+
+}