test: reorg #15698

Problem:
Subdirectories like "visual", "insert", "normal" encourage people to
separate *related* tests for no good reason.  Typically the _mode_ is
not the relevant topic of a test (and when it is, _then_ create
an appropriate describe() or it()).

Solution:
- Delete the various `test/functional/<mode>/` subdirectories, move
  their tests to more meaningful topics.
- Rename `…/normal/` to `…/editor/`.
  - Move or merge `…/visual/*` and `…/insert/*` tests into here where
    appropriate.
- Rename `…/eval/` to `…/vimscript/`.
  - Move `…/viml/*` into here also.

* test(reorg): insert/* => editor/mode_insert_spec.lua
* test(reorg): cmdline/* => editor/mode_cmdline_spec.lua
* test(reorg): eval core tests => eval_spec.lua

test/functional/editor/mode_insert_spec.lua

@@ -0,0 +1,89 @@
+-- Insert-mode tests.
+
+local helpers = require('test.functional.helpers')(after_each)
+local clear, feed, insert = helpers.clear, helpers.feed, helpers.insert
+local expect = helpers.expect
+local command = helpers.command
+local eq = helpers.eq
+local eval = helpers.eval
+local meths = helpers.meths
+
+describe('insert-mode', function()
+  before_each(function()
+    clear()
+  end)
+
+  it('CTRL-@', function()
+    -- Inserts last-inserted text, leaves insert-mode.
+    insert('hello')
+    feed('i<C-@>x')
+    expect('hellhello')
+
+    -- C-Space is the same as C-@.
+    -- CTRL-SPC inserts last-inserted text, leaves insert-mode.
+    feed('i<C-Space>x')
+    expect('hellhellhello')
+
+    -- CTRL-A inserts last inserted text
+    feed('i<C-A>x')
+    expect('hellhellhellhelloxo')
+  end)
+
+  describe('Ctrl-R', function()
+    it('works', function()
+      command("let @@ = 'test'")
+      feed('i<C-r>"')
+      expect('test')
+    end)
+
+    it('works with multi-byte text', function()
+      command("let @@ = 'påskägg'")
+      feed('i<C-r>"')
+      expect('påskägg')
+    end)
+  end)
+
+  describe('Ctrl-O', function()
+    it('enters command mode for one command', function()
+      feed('ihello world<C-o>')
+      feed(':let ctrlo = "test"<CR>')
+      feed('iii')
+      expect('hello worldiii')
+      eq(1, eval('ctrlo ==# "test"'))
+    end)
+
+    it('re-enters insert mode at the end of the line when running startinsert', function()
+      -- #6962
+      feed('ihello world<C-o>')
+      feed(':startinsert<CR>')
+      feed('iii')
+      expect('hello worldiii')
+    end)
+
+    it('re-enters insert mode at the beginning of the line when running startinsert', function()
+      insert('hello world')
+      feed('0<C-o>')
+      feed(':startinsert<CR>')
+      feed('aaa')
+      expect('aaahello world')
+    end)
+
+    it('re-enters insert mode in the middle of the line when running startinsert', function()
+      insert('hello world')
+      feed('bi<C-o>')
+      feed(':startinsert<CR>')
+      feed('ooo')
+      expect('hello oooworld')
+    end)
+
+    it("doesn't cancel Ctrl-O mode when processing event", function()
+      feed('iHello World<c-o>')
+      eq({mode='niI', blocking=false}, meths.get_mode()) -- fast event
+      eq(2, eval('1+1'))  -- causes K_EVENT key
+      eq({mode='niI', blocking=false}, meths.get_mode()) -- still in ctrl-o mode
+      feed('dd')
+      eq({mode='i', blocking=false}, meths.get_mode()) -- left ctrl-o mode
+      expect('') -- executed the command
+    end)
+  end)
+end)