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/vimscript/exepath_spec.lua

@@ -0,0 +1,40 @@
+local helpers = require('test.functional.helpers')(after_each)
+local eq, clear, call, iswin =
+  helpers.eq, helpers.clear, helpers.call, helpers.iswin
+local command = helpers.command
+local exc_exec = helpers.exc_exec
+local matches = helpers.matches
+
+describe('exepath()', function()
+  before_each(clear)
+
+  it('returns 1 for commands in $PATH', function()
+    local exe = iswin() and 'ping' or 'ls'
+    local ext_pat = iswin() and '%.EXE$' or '$'
+    matches(exe .. ext_pat, call('exepath', exe))
+    command('let $PATH = fnamemodify("./test/functional/fixtures/bin", ":p")')
+    ext_pat = iswin() and '%.CMD$' or '$'
+    matches('null' .. ext_pat, call('exepath', 'null'))
+    matches('true' .. ext_pat, call('exepath', 'true'))
+    matches('false' .. ext_pat, call('exepath', 'false'))
+  end)
+
+  it('fails for invalid values', function()
+    for _, input in ipairs({'""', 'v:null', 'v:true', 'v:false', '{}', '[]'}) do
+      eq('Vim(call):E928: String required', exc_exec('call exepath('..input..')'))
+    end
+    command('let $PATH = fnamemodify("./test/functional/fixtures/bin", ":p")')
+    for _, input in ipairs({'v:null', 'v:true', 'v:false'}) do
+      eq('Vim(call):E928: String required', exc_exec('call exepath('..input..')'))
+    end
+  end)
+
+  if iswin() then
+    it('append extension if omitted', function()
+      local filename = 'cmd'
+      local pathext = '.exe'
+      clear({env={PATHEXT=pathext}})
+      eq(call('exepath', filename..pathext), call('exepath', filename))
+    end)
+  end
+end)