tests and mocks for e2e testing (#78)

* tests and mocks for e2e testing

* formatting

* fix analyze errors

lib/src/support/platform.dart

@@ -1,9 +1,17 @@
+import 'dart:io';
+
+import 'package:meta/meta.dart';
+
 import 'platform/io.dart' if (dart.library.html) 'platform/web.dart';
 
 // Returns the current platform which works for both web and devices.
 PlatformType lkPlatform() => lkPlatformImplementation();
+
 bool lkPlatformIs(PlatformType type) => lkPlatform() == type;
 
+@internal
+bool lkPlatformIsTest() => Platform.environment.containsKey('FLUTTER_TEST');
+
 enum PlatformType {
   web,
   windows,