Fix the method for changing the Vimwiki syntax for tests.

This change ensures the syntax is properly changed when running multiple
tests by removing the previously created temporary wiki and then
creating a new one.

test/vader_includes/vader_setup.vader

@@ -1,7 +1,3 @@
-Execute (Setup):
-  " assumes 3 registered wikis in vimrc
-  let g:wiki_nr = 3
-
 Before (Define functions):
   " change the syntax using a temporary wiki
   function! SetSyntax(vw_syn)
@@ -21,9 +17,21 @@ Before (Define functions):
           \ 'ext': ext,
           \ 'syntax': a:vw_syn,
           \ }
+
+    " Remove any temporary wikis each time this function is called.
+    " This is necessary to ensure syntax is properly set when running multiple tests
+    " NOTE: this assumes there are 3 defined wikis in the vimrc. The last wiki
+    " contains default settings for temporary wikis (so there are always
+    " num wikis in vimrc + 1)
+    let num_wikis = len(g:vimwiki_wikilocal_vars)
+    while  num_wikis > 4
+      call remove(g:vimwiki_wikilocal_vars, num_wikis - 1)
+      let num_wikis = num_wikis - 1
+    endwhile
+
+    " add the new wiki
     call vimwiki#vars#add_temporary_wiki(new_temp_wiki_settings)
-    call vimwiki#vars#set_bufferlocal('wiki_nr', g:wiki_nr)
-    let g:wiki_nr += 1
+    call vimwiki#vars#set_bufferlocal('wiki_nr', 3)
 
     " verify syntax was set correctly
     Assert vimwiki#vars#get_wikilocal('syntax') ==# a:vw_syn, 'ERROR: Vimwiki syntax not set correctly.'
@@ -34,7 +42,7 @@ Before (Define functions):
     " clear mappings so plugin can be reloaded
     " this is needed if running manually multiple times
     nmapclear
-  
+
     unlet g:loaded_vimwiki
     source plugin/vimwiki.vim
   endfunction

test/vader_includes/vader_teardown.vader

@@ -1,4 +1,3 @@
-Execute (Cleanup):
+After (Cleanup):
   delfunction SetSyntax
   delfunction ReloadVimwiki
-  unlet g:wiki_nr