Skip failure test on pypy2 and make pypy2 mandatory
diff --git a/.travis.yml b/.travis.yml
index 4e5efed..ebcb0db 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -12,8 +12,6 @@
       dist: xenial
     - python: "nightly"
       dist: xenial
-  allow_failures:
-  - python: pypy
 install:
  - pip install -U pip
  - pip install -U wheel setuptools
diff --git a/mock/tests/testhelpers.py b/mock/tests/testhelpers.py
index ca31db3..2b2053f 100644
--- a/mock/tests/testhelpers.py
+++ b/mock/tests/testhelpers.py
@@ -4,6 +4,7 @@
 import socket
 
 import six
+import sys
 import time
 import unittest
 
@@ -459,6 +460,8 @@
             self._check_someclass_mock(mock)
 
 
+    @unittest.skipIf('PyPy' in sys.version and sys.version_info < (3, 0),
+                     "Fails on pypy2 due to incorrect signature for dict.pop from funcsigs")
     def test_builtin_functions_types(self):
         # we could replace builtin functions / methods with a function
         # with *args / **kwargs signature. Using the builtin method type