test: zero-length strings with path module functions

These testcases are specific to one uncommon behaviour in path module.
Few of the functions in path module, treat '' strings as current working
directory. This test makes sure that the behaviour is intact between
commits. See: #2106

test/parallel/test-path-zero-length-strings.js

@@ -0,0 +1,35 @@
+'use strict';
+
+// These testcases are specific to one uncommon behaviour in path module. Few
+// of the functions in path module, treat '' strings as current working
+// directory. This test makes sure that the behaviour is intact between commits.
+// See: https://github.com/nodejs/io.js/pull/2106
+
+const common = require('../common');
+const assert = require('assert');
+const path = require('path');
+const pwd = process.cwd();
+
+// join will internally ignore all the zero-length strings and it will return
+// '.' if the joined string is a zero-length string.
+assert.equal(path.join(''), '.');
+assert.equal(path.join('', ''), '.');
+assert.equal(path.join(pwd), pwd);
+assert.equal(path.join(pwd, ''), pwd);
+
+// normalize will return '.' if the input is a zero-length string
+assert.equal(path.normalize(''), '.');
+assert.equal(path.normalize(pwd), pwd);
+
+// Since '' is not a valid path in any of the common environments, return false
+assert.equal(path.isAbsolute(''), false);
+
+// resolve, internally ignores all the zero-length strings and returns the
+// current working directory
+assert.equal(path.resolve(''), pwd);
+assert.equal(path.resolve('', ''), pwd);
+
+// relative, internally calls resolve. So, '' is actually the current directory
+assert.equal(path.relative('', pwd), '');
+assert.equal(path.relative(pwd, ''), '');
+assert.equal(path.relative(pwd, pwd), '');