tests/test-check-clang-format.t

discovery-helper: add an extra argument to generate only one repo

This is useful to generate left and right in parallel when dealing with very
large repositories.

#require clang-format test-repo

  $ . "$TESTDIR/helpers-testrepo.sh"

  $ cd "$TESTDIR"/..
  $ for f in `testrepohg files 'set:(**.c or **.cc or **.h) and not "listfile:contrib/clang-format-ignorelist"'` ; do
  >   clang-format --style file $f > $f.formatted
  >   cmp $f $f.formatted || diff -u $f $f.formatted
  >   rm $f.formatted
  > done