tests/test-check-format.t

branchmap: make "closed" a set from beginning instead of converting from list

Differential Revision: https://phab.mercurial-scm.org/D7427

#require black

  $ cd $RUNTESTDIR/..
  $ black --config=black.toml --check --diff `hg files 'set:**.py - mercurial/thirdparty/** - "contrib/python-zstandard/**"'`