Before:
  Save g:ale_php_phpmd_executable

  unlet! g:ale_php_phpmd_executable

  runtime ale_linters/php/phpmd.vim

After:
  Restore

  call ale#linter#Reset()

Execute(Custom executables should be used for the executable and command):
  let g:ale_php_phpmd_executable = 'phpmd_test'

  AssertEqual 'phpmd_test', ale_linters#php#phpmd#GetExecutable(bufnr(''))
  AssertEqual
  \ ale#Escape('phpmd_test')
  \ . ' %s text cleancode,codesize,controversial,design,naming,unusedcode --ignore-violations-on-exit %t',
  \ ale_linters#php#phpmd#GetCommand(bufnr(''))