Never waste time. Boot MemTest86 from a USB drive and let it run overnight. One pass is insufficient. Eight passes is standard. Twenty-four passes is conclusive.
Shut down your Mac, press and hold the power button until you see "Loading startup options." Press Command + D to launch Apple Diagnostics. memory diagnostic tool
This article explains what memory diagnostic tools are, how they work, and which ones you should use. A memory diagnostic tool is a software utility that performs exhaustive read/write tests on your computer’s RAM modules. It writes specific patterns of data to each memory address, reads them back, and verifies that the data hasn’t been corrupted. Never waste time
It functions identically in practice—pre-OS, pattern-based exhaustive testing. Apple does not offer a third-party memory tester because Macs have integrated hardware diagnostics. Eight passes is standard