test: move format_{string,luav} to a separate module

test/functional/api/vim_spec.lua

@@ -34,7 +34,7 @@ local insert = helpers.insert
 local skip = helpers.skip
 
 local pcall_err = helpers.pcall_err
-local format_string = helpers.format_string
+local format_string = require('test.format_string').format_string
 local intchar2lua = helpers.intchar2lua
 local mergedicts_copy = helpers.mergedicts_copy
 local endswith = vim.endswith

test/functional/shada/merging_spec.lua

@@ -525,7 +525,7 @@ describe('ShaDa marks support code', function()
     local found = 0
     for _, v in ipairs(read_shada_file(shada_fname)) do
       if v.type == 7 and v.value.f == mock_file_path .. '-' then
-        print(require('test.helpers').format_luav(v))
+        print(require('test.format_string').format_luav(v))
         found = found + 1
       end
     end