Test coverage itself does not affect your app's runtime performance or battery life because tests run separately from the app. However, well-tested code tends to be more stable and efficient, indirectly improving user experience by reducing crashes and bugs.
Focus on writing unit and widget tests that cover UI rendering and logic without heavy dependencies. Use Flutter's flutter_test package to test widgets efficiently. Avoid long-running integration tests during development; run them separately. This keeps your development cycle fast and helps maintain smooth UI performance.
Test code is not included in your release app bundle, so it does not increase app size or startup time. Keeping tests separate ensures your app remains lightweight and fast to launch.
Flutter test coverage works the same on iOS and Android since tests run on the Dart VM or simulators/emulators. However, integration tests may require platform-specific setup for device permissions or UI interactions. Both platforms benefit equally from good test coverage to catch platform-specific bugs early.
Neither Apple App Store nor Google Play Store requires test coverage reports for app submission. However, Apple's Human Interface Guidelines emphasize app stability and quality, which good test coverage supports. Google Play encourages quality apps with fewer crashes, indirectly benefiting from tests.
It's likely your app has unoptimized code or heavy operations running on the main thread. Lack of test coverage might mean performance issues or bugs are undetected. Adding tests can help identify slow code paths or UI blocks causing delays.