Flutter automated testing

I am looking for a freelance Flutter developer with experience in automated testing. The project involves conducting integration tests for specific features of the Flutter app. The ideal candidate should have the following skills and experience:

- Familiarity with Flutter and its specific features, including user authentication, user interface interactions, and data retrieval and manipulation.
- Proficiency in conducting integration tests using.
- Ability to work with an existing test environment.

Please answer these questions.
1. How do you achieve this, any specific platforms you will use?
2. How will you test in hundreds of mobile?
3. Any process for setting up automated pipeline for testing multiple devices and versions?
4. Estimated costs of any 3rd party tools if used?

The main goal of this project is to ensure the seamless integration of different components of the Flutter app through automated testing. The developer should be able to identify and resolve any issues that may arise during the testing process.