test: add test-cases for posix path.relative()

adds posix test cases for paths similar to those that caused #5447 PR-URL: #5456 Reviewed-By: Brian White <[email protected]> Reviewed-By: Roman Reiss <[email protected]>

Author: omsmith

test/parallel/test-path.js

@@ -488,7 +488,9 @@ const relativeTests = [
 ['/var/','/var/lib','lib'],
 ['/','/var/lib','var/lib'],
 ['/foo/test','/foo/test/bar/package.json','bar/package.json'],
-['/Users/a/web/b/test/mails','/Users/a/web/b','../..']
+['/Users/a/web/b/test/mails','/Users/a/web/b','../..'],
+['/foo/bar/baz-quux','/foo/bar/baz','../baz'],
+['/foo/bar/baz','/foo/bar/baz-quux','../baz-quux']
 ]
 ]
 ];