nuageinit: add dirname edge case tests

libexec/nuageinit/tests/dirname.lua

@@ -1,11 +1,34 @@
 #!/usr/libexec/flua
+---
+-- SPDX-License-Identifier: BSD-2-Clause
+--
+-- Copyright (c) 2026 Baptiste Daroussin <bapt@FreeBSD.org>
 
 local n = require("nuage")
 
 print(n.dirname("/my/path/path1"))
+
+-- relative path with no directory component: nil
 if n.dirname("path") then
 	n.err('Expecting nil for n.dirname("path")')
 end
+
+-- nil input: nil
 if n.dirname() then
 	n.err("Expecting nil for n.dirname")
 end
+
+-- root path: returns "/"
+if n.dirname("/") ~= "/" then
+	n.err('Expecting "/" for n.dirname("/"), got: ' .. tostring(n.dirname("/")))
+end
+
+-- top-level directory: returns "/"
+if n.dirname("/foo") ~= "/" then
+	n.err('Expecting "/" for n.dirname("/foo")')
+end
+
+-- deep path
+if n.dirname("/foo/bar/baz") ~= "/foo/bar/" then
+	n.err('Expecting "/foo/bar/" for n.dirname("/foo/bar/baz")')
+end