Final answer:
Use Lenovo Bootable Diagnostics to test a machine without an operating system installed, as it is designed to work independently of the OS.
Step-by-step explanation:
If you need to run a diagnostics test on a customer's machine that currently has no operating system installed, the Lenovo diagnostics tool you could use is Lenovo Bootable Diagnostics. This tool can be run from a USB drive or another bootable device and is designed to work independently of an installed operating system, making it ideal for checking hardware functionality in bare-metal scenarios. Tools like the Lenovo Solution Center, Lenovo Diagnostics for Windows, and Lenovo Vantage require an operating system to be installed in order to function.