Before:
  Save g:ale_python_mypy_executable
  Save g:ale_python_mypy_options

  unlet! g:ale_python_mypy_executable
  unlet! g:ale_python_mypy_options

  runtime ale_linters/python/prospector.vim

After:
  Restore

  unlet! b:executable

  call ale#linter#Reset()

Execute(Setting executable to 'pipenv' appends 'run prospector'):
  let g:ale_python_prospector_executable = 'path/to/pipenv'

  AssertEqual
  \ ale#Escape('path/to/pipenv') . ' run prospector'
  \   .  '  --messages-only --absolute-paths --zero-exit --output-format json %s',
  \ ale_linters#python#prospector#GetCommand(bufnr(''))