Before:
  call ale#assert#SetUpLinterTest('asm', 'llvm_mc')
  call ale#test#SetFilename('test.cpp')
  let b:command_tail = ' --assemble'
  \   . ' --filetype=asm'
  \   . ' -o ' . (has('win32') ? 'nul': '/dev/null')
  \   . ' '

After:
  unlet! b:command_tail

  call ale#assert#TearDownLinterTest()

Execute(The default llvm-mc command should be correct):
  AssertLinter 'llvm-mc', ale#Escape('llvm-mc') . b:command_tail

Execute(The llvm-mc executable should be configurable):
  let b:ale_asm_llvm_mc_executable = 'foobar'

  AssertLinter 'foobar', ale#Escape('foobar') . b:command_tail