To test out a used MacBook before you buy, run Apple Diagnostics. It’s a built-in Apple tool that can help you detect issues with RAM, battery, sensors, graphics, CPU, and other hardware components. Here’s how to run Apple Diagnostics to test out a used MacBook before committing to a purchase:
Shut down your Mac and disconnect all peripherals
Press and hold the power button until the startup window appears
Press Command (⌘) + D
Wait for the test to complete and review the results