To deploy XCUITests you need locally build your test target and upload it to AppCenter

Prerequisites

The process currently requires the ownership of the repo. If you do not own the repo, use a fork.
You need to have the AppCenter-Cli installed. Install it via npm: npm install -g appcenter-cli
If you don't have Node.js installed, use this link

Procedure

If you do not already have an app on AppCenter to upload your tests to, navigate to AppCenter and create an app.

From within your app on AppCenter, navigate to Test > Test Runs and click New Test Run

The process for preparing and uploading your tests are outlined here

Troubleshooting

Building to Testing will require that your target be adequately signed & provisioned within Xcode. If errors arise, double check within Xcode to ensure that this has been done properly

If the build succeeds but the test fails, double check within the directory YOUR_PROJECT_ROOT/DerivedData/Build/Products/Debug-iphoneos/ for the build product TEST_TARGET_NAME-Runner.app. Sometimes the build will run correctly without generating this product. If the build passes but the test upload fails, check to see if this build product is missing. If it is, delete the DerivedData folder from within your project root and restart the process.