Add a test to cover sign placement after linting

test/test_sign_placement.vader

@@ -0,0 +1,68 @@
+Before:
+  function! GenerateResults(buffer, output)
+    return [
+    \ {
+    \   'lnum': 1,
+    \   'col': 1,
+    \   'bufnr': bufnr('%'),
+    \   'vcol': 0,
+    \   'nr': -1,
+    \   'type': 'E',
+    \   'text': 'foo',
+    \ },
+    \ {
+    \   'lnum': 2,
+    \   'col': 1,
+    \   'bufnr': bufnr('%'),
+    \   'vcol': 0,
+    \   'nr': -1,
+    \   'type': 'W',
+    \   'text': 'bar',
+    \ },
+    \ {
+    \   'lnum': 3,
+    \   'col': 1,
+    \   'bufnr': bufnr('%'),
+    \   'vcol': 0,
+    \   'nr': -1,
+    \   'type': 'E',
+    \   'text': 'baz',
+    \ },
+    \]
+  endfunction
+
+  call ale#linter#Define('testft', {
+  \ 'name': 'x',
+  \ 'executable': 'echo',
+  \ 'command': 'echo',
+  \ 'callback': 'GenerateResults',
+  \})
+
+After:
+  call ale#linter#Reset()
+  delfunction GenerateResults
+  unlet! g:output
+
+Given testft(A Javscript file with warnings/errors):
+  foo
+  bar
+  baz
+
+Execute:
+  call ale#Lint()
+  call ale#engine#WaitForJobs(2000)
+
+  redir => g:output
+    :sign place
+  redir END
+
+  AssertEqual
+  \ [
+  \   ['1', '1000001', 'ALEErrorSign'],
+  \   ['2', '1000002', 'ALEWarningSign'],
+  \   ['3', '1000003', 'ALEErrorSign'],
+  \ ],
+  \ map(
+  \   split(g:output, '\n')[2:],
+  \   'matchlist(v:val, "[^=]*=\\(\\d\\+\\)[^=]*=\\(\\d\\+\\).*\\(ALE.*\\)$")[1:3]'
+  \ )