test: replace busted with local harness

Replace the busted-based Lua test runner with a repo-local harness.

The new harness runs spec files directly under `nvim -ll`, ships its own
reporter and lightweight `luassert` shim, and keeps the helper/preload
flow used by the functional and unit test suites.

Keep the file boundary model shallow and busted-like by restoring `_G`,
`package.loaded`, `package.preload`, `arg`, and the process environment
between files, without carrying extra reset APIs or custom assertion
machinery.

Update the build and test entrypoints to use the new runner, add
black-box coverage for the harness itself, and drop the bundled
busted/luacheck dependency path.

AI-assisted: Codex

1 files changed, 35 insertions, 0 deletions

diff --git a/test/runner.lua b/test/runner.lua
new file mode 100644
index 0000000000..a73719893d
--- /dev/null
+++ b/test/runner.lua
@@ -0,0 +1,35 @@
+local uv = vim.uv
+
+---@return string
+local function repo_root()
+  local source = debug.getinfo(1, 'S').source
+  assert(type(source) == 'string' and vim.startswith(source, '@'), 'failed to resolve runner path')
+  local script_path = assert(uv.fs_realpath(source:sub(2)), 'failed to resolve runner path')
+  return vim.fs.dirname(vim.fs.dirname(script_path))
+end
+
+---@param roots string[]
+local function prepend_package_roots(roots)
+  local entries = {}
+  for _, root in ipairs(roots) do
+    entries[#entries + 1] = root .. '/?.lua'
+    entries[#entries + 1] = root .. '/?/init.lua'
+  end
+
+  package.path = table.concat(entries, ';') .. ';' .. package.path
+end
+
+_G.c_include_path = {}
+while _G.arg[1] and vim.startswith(_G.arg[1], '-I') do
+  table.insert(_G.c_include_path, string.sub(table.remove(_G.arg, 1), 3))
+end
+
+local root = repo_root()
+prepend_package_roots({ root, root .. '/test', '.', './test' })
+
+local exit_code = require('test.harness').main(_G.arg)
+io.stdout:flush()
+io.stderr:flush()
+
+-- Close the standalone Lua state before exit so sanitizers see Lua-owned cleanup.
+os.exit(exit_code, true)