Integration tests (end to end tests)

A recent version of the [integration_test](https://pub.dev/packages/integration_test) package has been published which means the following guide is not up to date: https://flutter.dev/docs/cookbook/testing/integration/introduction

Instead follow the steps on https://flutter.dev/docs/testing/integration-tests

See also the following commit which show how to create a new task inside a test: https://github.com/dwyl/flutter-todo-list-tutorial/pull/17/commits/33063b819c4c9ec812e421d2f74825c68ee73a7f

To run the test run `flutter drive --driver=test_driver/integration_test.dart --target=integration_test/todolist_test.dart`