encoding: Update handling of encoding in tests

Always run tests with encoding=utf-8, regardless of user locale
Don't set &encoding after startup in tests

Helped-By: Michael Reed <m.reed@mykolab.com>

test/functional/helpers.lua

@@ -7,7 +7,7 @@ local Session = require('nvim.session')
 
 local nvim_prog = os.getenv('NVIM_PROG') or 'build/bin/nvim'
 local nvim_argv = {nvim_prog, '-u', 'NONE', '-i', 'NONE', '-N',
-                   '--cmd', 'set shortmess+=I background=light noswapfile noautoindent laststatus=1',
+                   '--cmd', 'set shortmess+=I background=light noswapfile noautoindent laststatus=1 encoding=utf-8',
                    '--embed'}
 
 -- Formulate a path to the directory containing nvim.  We use this to

test/functional/legacy/044_099_regexp_multibyte_magic_spec.lua

@@ -33,7 +33,6 @@ local function run_test_with_regexpengine(regexpengine)
     j 0123❤x
     k combinations]])
 
-  execute('set encoding=utf-8')
   execute('set re=' .. regexpengine)
 
   -- Lines 1-8. Exercise regexp search with various magic settings. On each

test/functional/legacy/075_maparg_spec.lua

@@ -10,7 +10,6 @@ describe('maparg()', function()
 
   it('is working', function()
     execute('set cpo-=<')
-    execute('set encoding=utf8')
 
     -- Test maparg() with a string result
     execute('map foo<C-V> is<F4>foo')

test/functional/legacy/082_string_comparison_spec.lua

@@ -9,7 +9,6 @@ describe('case-insensitive string comparison in UTF-8', function()
   setup(clear)
 
   it('is working', function()
-    execute('set enc=utf8')
     feed('ggdG<cr>')
     source([[
       function! Ch(a, op, b, expected)

test/functional/legacy/095_regexp_multibyte_spec.lua

@@ -15,7 +15,7 @@ describe('regex with multi-byte', function()
       Results of test95:]])
 
     source([=[
-      set encoding=utf-8 nomore
+      set nomore
       let tl = []
 
       call add(tl, [2, '[[:alpha:][=a=]]\+', '879 aiaãâaiuvna ', 'aiaãâaiuvna'])

test/functional/legacy/mapping_spec.lua

@@ -12,8 +12,6 @@ describe('mapping', function()
       test starts here:
       ]])
 
-    execute('set encoding=utf-8')
-
     -- Abbreviations with р (0x80) should work.
     execute('inoreab чкпр   vim')
     feed('GAчкпр <esc>')

test/functional/legacy/utf8_spec.lua

@@ -10,7 +10,6 @@ describe('utf8', function()
   it('is working', function()
     insert('start:')
 
-    execute('set encoding=utf-8')
     execute('new')
     execute('call setline(1, ["aaa", "あああ", "bbb"])')