feat(lua): add vim.spell (#16620)

test/functional/lua/spell_spec.lua

@@ -0,0 +1,53 @@
+local helpers = require('test.functional.helpers')(after_each)
+local clear = helpers.clear
+local exec_lua = helpers.exec_lua
+local eq = helpers.eq
+local pcall_err = helpers.pcall_err
+
+describe('vim.spell', function()
+  before_each(function()
+    clear()
+  end)
+
+  describe('.check', function()
+    local check = function(x, exp)
+        return eq(exp, exec_lua("return vim.spell.check(...)", x))
+    end
+
+    it('can handle nil', function()
+      eq([[Error executing lua: [string "<nvim>"]:0: bad argument #1 to 'check' (expected string)]],
+        pcall_err(exec_lua, [[vim.spell.check(nil)]]))
+    end)
+
+    it('can check spellings', function()
+      check('hello', {})
+
+      check(
+        'helloi',
+        {{"helloi", "bad", 1}}
+      )
+
+      check(
+        'hello therei',
+        {{"therei", "bad", 7}}
+      )
+
+      check(
+        'hello. there',
+        {{"there", "caps", 8}}
+      )
+
+      check(
+        'neovim cna chkc spellins. okay?',
+        {
+          {"neovim"  , "bad" ,  1},
+          {"cna"     , "bad" ,  8},
+          {"chkc"    , "bad" , 12},
+          {"spellins", "bad" , 17},
+          {"okay"    , "caps", 27}
+        }
+      )
+    end)
+
+  end)
+end)