Before:
  runtime ale_linters/elixir/mix.vim
  call ale#test#SetFilename('/testplugin/lib/foo.ex')

After:
  call ale#linter#Reset()

Execute(The mix handler should parse lines correctly):
  let input_lines = [
  \ '    warning: variable "a" is unused (if the variable is not meant to be used, prefix it with an underscore)',
  \ '    │',
  \ ' 16 │     a = missing_var',
  \ '    │     ~',
  \ '    │',
  \ '    └─ /testplugin/lib/foo.ex:16:5: Foo.hello/0',
  \ '',
  \ '    warning: variable "b" is unused (if the variable is not meant to be used, prefix it with an underscore)',
  \ '    │',
  \ ' 17 │     b = another_missing_var',
  \ '    │     ~',
  \ '    │',
  \ '    └─ /testplugin/lib/foo.ex:17:5: Foo.hello/0',
  \ '',
  \ '    error: undefined variable "another_missing_var"',
  \ '    │',
  \ ' 17 │     b = another_missing_var',
  \ '    │         ^^^^^^^^^^^^^^^^^^^',
  \ '    │',
  \ '    └─ /testplugin/lib/foo.ex:17:9: Foo.hello/0',
  \ '',
  \ '    error: undefined variable "missing_var"',
  \ '    │',
  \ ' 16 │     a = missing_var',
  \ '    │         ^^^^^^^^^^^',
  \ '    │',
  \ '    └─ /testplugin/lib/foo.ex:16:9: Foo.hello/0',
  \ '',
  \ '    error: undefined variable "unrelated_var"',
  \ '    │',
  \ ' 16 │     a = unrelated_var',
  \ '    │         ^^^^^^^^^^^',
  \ '    │',
  \ '    └─ /testplugin/lib/unrelated.ex:16:9: Foo.hello/0',
  \ '',
  \ '',
  \ '== Compilation error in file /testplugin/lib/foo.ex ==',
  \ '** (CompileError) /testplugin/lib/foo.ex: cannot compile module Foo (errors have been logged)',
  \ ]

  AssertEqual
  \ [
  \   {
  \     'bufnr': bufnr(''),
  \     'lnum': 16,
  \     'col': 5,
  \     'type': 'W',
  \     'text': 'variable "a" is unused (if the variable is not meant to be used, prefix it with an underscore)',
  \     'detail': join(input_lines, "\n"),
  \   },
  \   {
  \     'bufnr': bufnr(''),
  \     'lnum': 17,
  \     'col': 5,
  \     'type': 'W',
  \     'text': 'variable "b" is unused (if the variable is not meant to be used, prefix it with an underscore)',
  \     'detail': join(input_lines, "\n"),
  \   },
  \   {
  \     'bufnr': bufnr(''),
  \     'lnum': 17,
  \     'col': 9,
  \     'type': 'E',
  \     'text': 'undefined variable "another_missing_var"',
  \     'detail': join(input_lines, "\n"),
  \   },
  \   {
  \     'bufnr': bufnr(''),
  \     'lnum': 16,
  \     'col': 9,
  \     'type': 'E',
  \     'text': 'undefined variable "missing_var"',
  \     'detail': join(input_lines, "\n"),
  \   },
  \ ],
  \ ale_linters#elixir#mix#Handle(bufnr(''), input_lines)