docs: def set_env(self):
          """Put info about coverage into the env so that subprocesses can activate coverage."""
  
          if self.cov_source is None:
              os.environ['COV_CORE_SOURCE'] = ''
          else:
              os.environ['COV_CORE_SOURCE'] = UNIQUE_SEP.join(self.cov_source)
          os.environ['COV_CORE_DATA_FILE'] = self.cov_data_file
          os.environ['COV_CORE_CONFIG'] = self.cov_config