Tests: Added GTests for base/callback.cc

Change-Id: Icebd0fdec4be86e0f0fd86ef58f52ddbfdf8d714
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/21619
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>
2 files changed