Stereo Test is the simplest, yet the most convenient (and least startling) app for testing whether both of your speakers are functional and oriented correctly.. or if you placed each headphone in the right ear.

If you have a phone, or tablet with stereo speakers, this app will help you check if both speakers are playing correctly and equally loud.

If you just placed your headphones in your ears and the fit is perfect but you aren't sure whether "Right" is REALLY right, this app will tell you without the need to remove the headphones.

If you have an external, stereo set-up, you can easily check whether the left and right speakers have been placed correctly and/or are functional.

"Left" channel sound is really just 100% left, and right is really just 100% right. Same sound, same volume, constant sound, no confusing transitions.

The "Stereo Test for speakers & headphones" is simple yet fills several gaps that bothered me with available apps - most of them had transitions or leakage between channels leading to "false positives", while there was no way to toggle between just playing a constant sound on a given channel (so I could tinker with my speakers until I could hear the sound correctly) and just a short sound (~20 seconds) that would stop playing by itself so I can determine which headphone is "right", jump out of the app and straight into the music with no need to close the app.
This Stereo Sound Test has a setting for that and does both.

Additionally, the sound is pulsating, constant and a few tones quieter than music would be at the same volume level of your device, making it the least startling stereo tester.

If you're looking for an app that will perform a stereo test of your audio channels / check your sound set-up with no data connection required, well, here you go, welcome the Stereo Test! I hope you will find it useful, and thanks for giving it a try!

Credits: App icon courtesy of Vecteezy.com