This error appears because an earlier version of Node is installed on your computer.
CLI Mobile Center mobile-center requires the latest version of Node.
Here are the steps I used to fix this error:
/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
Update the latest version of Node by typing these commands into the terminal
sudo brew uninstall node brew update brew upgrade brew cleanup brew install node sudo chown -R $(whoami) /usr/local brew link
Uninstall / reinstall mobile-center-cli to make sure you have the latest version of the CLI Mobile Center by entering these commands in the terminal
npm uninstall -g mobile-center-cli npm install -g mobile-center-cli
Log in to the mobile center through the CLI by entering this command in your terminal *
mobile-center login
Now you can upload your UITests to the mobile center using the CLI
mobile-center test run uitest --app [appname] --devices [deviceID] --app-path [LocationOfYourAppOnYour] --test-series "master" --locale "en_US" --assembly-dir [FolderContainingUITestDLL]
* If you have not created a password to log in to your mobile center, go to mobile.azure.com , mobile.azure.com out of your account if you are currently logged in, and then click "Forgot your password?". to create a password for your Mobile Center account.

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