add test for md5 implementation

spec/unit/md5_spec.lua

@@ -0,0 +1,12 @@
+require("commonrequire")
+
+local md5 = require("MD5")
+
+describe("MD5 module", function()
+    it("should calculate correct MD5 hashes", function()
+        assert.is_equal(md5(""), "d41d8cd98f00b204e9800998ecf8427e")
+        assert.is_equal(md5("\0"), "93b885adfe0da089cdf634904fd59f71")
+        assert.is_equal(md5("0123456789abcdefX"), "1b05aba914a8b12315c7ee52b42f3d35")
+    end)
+end)
+