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_cmdline_spec.lua

@@ -0,0 +1,69 @@
+-- Cmdline-mode tests.
+
+local helpers = require('test.functional.helpers')(after_each)
+local clear, insert, funcs, eq, feed =
+  helpers.clear, helpers.insert, helpers.funcs, helpers.eq, helpers.feed
+local meths = helpers.meths
+
+describe('cmdline CTRL-R', function()
+  before_each(clear)
+
+  it('pasting non-special register inserts <CR> *between* lines', function()
+    insert([[
+    line1abc
+    line2somemoretext
+    ]])
+    -- Yank 2 lines linewise, then paste to cmdline.
+    feed([[<C-\><C-N>gg0yj:<C-R>0]])
+    -- <CR> inserted between lines, NOT after the final line.
+    eq('line1abc\rline2somemoretext', funcs.getcmdline())
+
+    -- Yank 2 lines charwise, then paste to cmdline.
+    feed([[<C-\><C-N>gg05lyvj:<C-R>0]])
+    -- <CR> inserted between lines, NOT after the final line.
+    eq('abc\rline2', funcs.getcmdline())
+
+    -- Yank 1 line linewise, then paste to cmdline.
+    feed([[<C-\><C-N>ggyy:<C-R>0]])
+    -- No <CR> inserted.
+    eq('line1abc', funcs.getcmdline())
+  end)
+
+  it('pasting special register inserts <CR>, <NL>', function()
+    feed([[:<C-R>="foo\nbar\rbaz"<CR>]])
+    eq('foo\nbar\rbaz', funcs.getcmdline())
+  end)
+end)
+
+describe('cmdline history', function()
+  before_each(clear)
+
+  it('correctly clears start of the history', function()
+    -- Regression test: check absence of the memory leak when clearing start of
+    -- the history using ex_getln.c/clr_history().
+    eq(1, funcs.histadd(':', 'foo'))
+    eq(1, funcs.histdel(':'))
+    eq('', funcs.histget(':', -1))
+  end)
+
+  it('correctly clears end of the history', function()
+    -- Regression test: check absence of the memory leak when clearing end of
+    -- the history using ex_getln.c/clr_history().
+    meths.set_option('history', 1)
+    eq(1, funcs.histadd(':', 'foo'))
+    eq(1, funcs.histdel(':'))
+    eq('', funcs.histget(':', -1))
+  end)
+
+  it('correctly removes item from history', function()
+    -- Regression test: check that ex_getln.c/del_history_idx() correctly clears
+    -- history index after removing history entry. If it does not then deleting
+    -- history will result in a double free.
+    eq(1, funcs.histadd(':', 'foo'))
+    eq(1, funcs.histadd(':', 'bar'))
+    eq(1, funcs.histadd(':', 'baz'))
+    eq(1, funcs.histdel(':', -2))
+    eq(1, funcs.histdel(':'))
+    eq('', funcs.histget(':', -1))
+  end)
+end)