These are the packages that would be merged, in order:

Calculating dependencies ... done!
Dependency resolution took 0.98 s (backtrack: 0/20).

[ebuild  N     ] dev-cpp/catch-3.15.3::gentoo  USE="-test" 1181 KiB
[ebuild  N     ] dev-libs/libmcfp-1.4.2::gentoo  USE="-test" 35 KiB

Total: 2 packages (2 new), Size of downloads: 1215 KiB