test(harness): migrate away from magic globals

Problem:
The magic globals `it`, `describe`, etc., are more trouble than they are
worth.

- Hooking into `after_each` requires `getfenv()` hacks.
- They confuse luals/emmylua, because the top-level `.luarc.json` isn't
  merged with `test/.luarc.json` (apparently a luals limitation?)
- They totally defeat discoverability because the user just has to
  "know" about the various magic symbols.

So they harm DX, which means they serve no purpose at all.

Solution:
- Expose the test API from `testutil`, so tests can call `t.it()`,
  `t.describe()`, etc., in the conventional way.
- Drop `getfenv()` hacks.
- Drop the `setfenv()` injection in `load_chunk`.
- Drop `test/_meta.lua`.

1 files changed, 2 insertions, 0 deletions

diff --git a/test/functional/vimscript/executable_spec.lua b/test/functional/vimscript/executable_spec.lua
index 4101d8f32d..7b3f81fb7c 100644
--- a/test/functional/vimscript/executable_spec.lua
+++ b/test/functional/vimscript/executable_spec.lua
@@ -1,6 +1,8 @@
 local t = require('test.testutil')
 local n = require('test.functional.testnvim')()
 
+local describe, it, before_each, setup, teardown, pending =
+  t.describe, t.it, t.before_each, t.setup, t.teardown, t.pending
 local eq, clear, call, write_file, command = t.eq, n.clear, n.call, t.write_file, n.command
 local eval, fn = n.eval, n.fn
 local is_os = t.is_os