Before:
  runtime ale_linters/ruby/rubocop.vim

Execute(Executable should default to rubocop):
  AssertEqual
  \ '''rubocop'' --format emacs --force-exclusion  --stdin ''dummy.py''',
  \ ale_linters#ruby#rubocop#GetCommand(bufnr(''))

Execute(Should be able to set a custom executable):
  let g:ale_ruby_rubocop_executable = 'bin/rubocop'
  AssertEqual
  \ '''bin/rubocop'' --format emacs --force-exclusion  --stdin ''dummy.py''',
  \ ale_linters#ruby#rubocop#GetCommand(bufnr(''))

Execute(Setting bundle appends 'exec rubocop'):
  let g:ale_ruby_rubocop_executable = 'path to/bundle'
  AssertEqual
  \ '''path to/bundle'' exec rubocop --format emacs --force-exclusion  --stdin ''dummy.py''',
  \ ale_linters#ruby#rubocop#GetCommand(bufnr(''))