message: go: Don't `exit` from a library.
  Really, don't.
diff: @@ -170,13 +170,13 @@ class Toolkit(dict):
  else:
  for entry in Toolkit.properties:
  super().__init__(**{
  - entry: values[entry] or environ.get('GO%s' % entry.upper()) for entry in Toolkit.properties
  + entry: values[entry] or environ.get('GO%s' % entry.upper())
  + for entry in Toolkit.properties
  })
  try:
  self.run(['help'])
  except FileNotFoundError:
  - import sys
  - sys.exit("Error:\n Go not found, make sure Go is installed and is referenced in your PATH.")
  + raise Exception('go executable not found')
  @property
  def env(self):
  