First and most generic rule: just look around.
But, we have a script for checking patches/files/git-refs:
# Chech HEAD git ref
./checkpatch.sh -r
./checkpatch.sh -r HEAD
# Check patch
git format-patch --stdout -1 | ./checkpatch.sh -p
git show -1 | ./checkpatch.sh -p
# Or via regular files
git format-patch --stdout -2
./checkpatch.sh *.patch
# Over a file
./checkpatch.sh -d event.c
./checkpatch.sh -d < event.c
# And print the whole file not only summary
./checkpatch.sh -f event.c
./checkpatch.sh -f < event.c
# See
./checkpatch.sh -h
- Write new unit test in
test/regress_{MORE_SUITABLE_FOR_YOU}.c
make verify