I guess it was because after run instrumented test file so become can't open Android Studio's emulator? But I am not sure.
Error message: Launching 'app' on No Devices. Error while waiting for device: The emulator process for AVD Pixel_4_XL_API_30 was killed.

I used follow solution solved this problem.↓
Tools -> SDK Manager -> SDK Tools (tab) -> Deselect 'Android Emulator' -> OK
Now, when you try to run your app, or launch device from AVD Manager, it will give the 'Install Emulator' error -> Click Ok. This will automatically download the correct version.
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