What app can you install to allow you to use your mobile device to test your mobile controls within the Unity editor?

The correct choice is Unity Remote, which is an application specifically designed to facilitate the testing of mobile controls directly within the Unity editor. This tool enables developers to connect their mobile device to the Unity editor via USB or a network and interact with the game. It allows developers to get immediate feedback on touch input, accelerometer data, and other mobile-specific functionality without the need to build and deploy the game to the mobile device each time they want to test a change.

Unity Remote acts as a bridge between the Unity editor and the mobile device, allowing for quick iterations during the development phase. This is especially useful for ensuring that the user interface and controls feel responsive and intuitive on mobile devices, where the experience may differ significantly from desktop environments.

The other options do not serve this purpose. Unity Connect was a networking tool that connected developers with opportunities and resources. Unity Cloud Build is a service for automating the build process for different platforms but does not facilitate direct testing of controls. Unity Editor Remote does not exist as a recognized application in Unity's suite of tools. Therefore, using Unity Remote is the best choice for testing mobile controls in the Unity editor.