How to test your app while not effecting active users?

I am soon ready to release my app on the play store but I would like to know how can I edit/add features/update my app without affecting my users. For example if I decided to add or remove something from the server I don't want the whole app to crash on the users. Basically running a clone where I can try out anything I want and it stays separate from the original app. How do I do that?

I am really sorry if I confused you all and my English is not the best.

For that you would run a development server and have multiple builds of your app.

You can use google play to distribute that app to your test users, described here or you can manually install the app on test devices. Manually installing is faster(if you have a few test users) than waiting for google play to push an update.

As for how to set it up, that would depend on what you are doing and with what tools. Usually you would set up multiple builds in android with BuildConfig.java variables. There you can either check the build type and use a specific API key/Server URL or you can pass a different value depending on the build. More info here.

Basically in your build.gradle you would have:

android {
    ...
    buildTypes {
        release {
            buildConfigField("String", "SERVER_URL", "https://api.example.com/")
        }
        debug {
            buildConfigField("String", "SERVER_URL", "https://api.dev.example.com")
        }
    }
}

You can switch which variant you are building from Build > Select Build Variant... or from the sidebar in Android Studio

Now you can access these from your code as:

BuildConfig.SERVER_URL

Next you would distribute that app to your test users.

As for the server side it depends on how you have it set up now and how you want to set it up.

Google Play’s Core library (on 1.5.0 or higher) has a feature for apps running on devices using Android 5.0 (API level 21) or higher and Chrome OS devices, called In-app updates. If you want users to try a new app feature or apply updates to improve performance or fix bugs, the Play Core library offers two methods. You can notify users about an available update using the Flexible or Immediate approach.

The In-app updates has a new request flow for you to prompt active users to update the app. Using the Flexible approach, the update is downloaded and installed in the background while the app is still in use. With the Immediate option, the user has to accept the update request after which Google Play manages the installation and restart the app.

Set a priority for each update in the Google Play Developer API, which determines how your app recommends an update, using an integer value between 0 and 5, with the default being 0 and 5 being the highest priority.