diff -up ./tests/test_mex.py.orig ./tests/test_mex.py
--- ./tests/test_mex.py.orig	2018-10-19 00:29:42.000000000 +0200
+++ ./tests/test_mex.py	2018-11-02 01:34:24.851553069 +0100
@@ -25,6 +25,7 @@
 #
 #------------------------------------------------------------------------------
 import os
+from distutils.version import LooseVersion
 import unittest
 import httpretty
 from tests import util
@@ -52,7 +53,10 @@ class Test_Mex(unittest.TestCase):
             mex.discover()
             self.fail('No exception was thrown caused by failed request')
         except Exception as exp:
-            self.assertEqual(exp.args[0], 'Mex Get request returned http error: 500 and server response: HTTPretty :)')
+            if LooseVersion(httpretty.__version__) >= LooseVersion("0.9.0"):
+                self.assertEqual(exp.args[0], 'Mex Get request returned http error: 500 and server response: {"message": "HTTPretty :)"}')
+            else:
+                self.assertEqual(exp.args[0], 'Mex Get request returned http error: 500 and server response: HTTPretty :)')
 
     @httpretty.activate
     def _happyPathTest(self, file_name, expectedUrl):