Implementing OAuth2 authentication with a browser popup for automated testing in an Android Emulator presents challenges that were addressed in the development of the FusionAuth Android SDK. The blog outlines the importance of end-to-end testing using a real FusionAuth backend to ensure the reliability and seamless integration of authentication and authorization features in Android apps. By moving away from traditional mocking, which can obscure real-world issues, and instead utilizing a "local-first" approach with actual login flows, the testing framework catches regressions early and improves confidence in the application's functionality. The testing strategy involves converting manual interactions into automated scripts executed within the IDE, integrating tests into GitHub workflows for consistent checks against updates, and setting up an environment that includes multiple Android versions and emulators. This comprehensive testing approach, coupled with GitHub automation and Dependabot configurations for dependency management, ensures thorough validation and maintains high standards of quality and reliability for the SDK, which is critical for a secure user experience in mobile apps.