code: function fixturizeCommitSha (map, sha) {
    // Do nothing if the passed sha is already set
    if (map[sha]) {
      return map[sha]
    }
  
    // Do nothing if the passed sha is one of our fixturized ones
    if (Object.values(map).includes(sha)) {
      return sha
    }
  
    // Otherwise calculate the new sha and set it on the passed state map.
    const counter = Object.keys(map).length + 1
    map[sha] = ('0000000000000000000000000000000000000000' + counter).substr(-40)
  
    return map[sha]
  }
docs: We keep track of commit sha hashes. We don’t want to simply zerofy them as there can be multiple commits. So instead we keep state of a counter and pad the counter with 0s left.