If you do a mockbuild with fedpkg --release f27 mockbuild -N, afterwards you can enter the chroot for debugging with mock -N -r fedora-27-x86_64 --shell. The mapping of --release values to -r values is simple, but if for example --release is not explicitly given but inferred from the checked out Git branch, it is easy to mix up the different chroots and be confused why the results of fedpkg mockbuild differ from the interactive session in mock --shell.

Therefore it would be nice if (for example) an option --shell would be added tofedpkg mockbuild that is passed on to mock in addition to the values determined for -r, etc. so that fedpkg mockbuild -N; fedpkg mockbuild -N --shell will open a shell in the chroot that the build was just executed in.