- given: "an installed Bumper"
  function: install_bumper

- given: "all files in {dirname} are committed to git"
  function: git_init_and_commit_everything

- given: "the HEAD commit in {dirname} is {varname}"
  function: remember_HEAD
  
- when: "I run, in {dirname}, {argv0}{args:text}"
  function: run_command_in_directory

- then: "in {dirname}, git tag {tag} is a signed tag pointing at <{varname}>"
  function: git_tag_points_at