Add vader tests and docker setup

test/tabnext_delay.vader

@@ -0,0 +1,31 @@
+Before (Setup):
+  let g:vimwiki_folding = 'expr:quick'
+
+  " clear mappings so plugin can be reloaded
+  " this is needed if running manually multiple times
+  nmapclear
+
+  " reload the plugin to set the fold method
+  unlet g:loaded_vimwiki
+  source plugin/vimwiki.vim
+
+Execute (Expect < 0.5 second delay: Issue #580):
+  " prep
+  edit test/resources/delay.wiki
+  normal! 50%
+  normal! zozo
+  tabedit
+
+  " run test
+  let start = reltime()
+  tabprev
+  redraw
+  let end = str2float(reltimestr(reltime(start)))
+
+  " cleanup
+  bdelete test/resources/delay.wiki
+  tabclose
+
+  " verify
+  Log 'Elapsed time = ' . string(end)
+  Assert end < 0.5, 'Took longer than expected: ' . string(end) . ' seconds'