Try to work around some test issues in PyPy3:

- CyFunction seems to lead to deeper stacks on recursion.
- Passing integers through call layers can end up creating new int objects instead of keeping the identical objects ('is' test fails)'.

tests/run/isnot.pyx

@@ -3,12 +3,17 @@
 
 cimport cython
 
+# Use a single global object for identity checks.
+# PyPy can optimise away integer objects, for example, and may fail the 'is' test.
+obj = object()
+
+
 @cython.test_fail_if_path_exists('//NotNode')
 def is_not(a, b):
     """
     >>> is_not(1, 2)
     True
-    >>> x = 1
+    >>> x = obj
     >>> is_not(x, x)
     False
     """
@@ -20,7 +25,7 @@ def not_is_not(a, b):
     """
     >>> not_is_not(1, 2)
     False
-    >>> x = 1
+    >>> x = obj
     >>> not_is_not(x, x)
     True
     """
@@ -32,7 +37,7 @@ def not_is(a, b):
     """
     >>> not_is(1, 2)
     True
-    >>> x = 1
+    >>> x = obj
     >>> not_is(x, x)
     False
     """

tests/run/knuth_man_or_boy_test.pyx

@@ -46,9 +46,13 @@ def compute(val):
 def a(in_k, x1, x2, x3, x4, x5):
     """
     >>> import sys
-    >>> sys.setrecursionlimit(1350)
+    >>> old_limit = sys.getrecursionlimit()
+    >>> sys.setrecursionlimit(1350 if not getattr(sys, 'pypy_version_info', None) else 2700)
+
     >>> a(10, 1, -1, -1, 1, 0)
     -67
+
+    >>> sys.setrecursionlimit(old_limit)
     """
     k = [in_k]
     def b():