Add test for helptags

test/help.vim

@@ -0,0 +1,36 @@
+let s:suite = themis#suite('help')
+
+function! s:suite.after() abort
+  if filereadable('doc/tags')
+    call delete('doc/tags')
+  endif
+endfunction
+
+function! s:suite.make_helptags() abort
+  " Detect E154
+  helptags doc
+endfunction
+
+function! s:suite.__modules__() abort
+  let modules = themis#suite('helptags for module')
+
+  function! modules.before() abort
+    helptags doc
+  endfunction
+
+  function! modules.__each_modules__() abort
+    let V = vital#of('vital')
+    for module_name in V.search('**')
+      let module = V.import(module_name)
+      let suite = themis#suite(module_name)
+      for func_name in keys(module)
+        let tagname = printf('Vital.%s.%s()', module_name, func_name)
+        execute join([
+        \   printf('function! suite.%s()', func_name),
+        \   printf('  help %s', tagname),
+        \   'endfunction',
+        \ ], "\n")
+      endfor
+    endfor
+  endfunction
+endfunction