Issue #20532: Tests which use _testcapi now are marked as CPython only.

20 files changed, 204 insertions, 103 deletions

diff --git a/Lib/test/string_tests.py b/Lib/test/string_tests.py
index 837c1e8..0479601 100644
--- a/Lib/test/string_tests.py
+++ b/Lib/test/string_tests.py
@@ -5,7 +5,6 @@ Common tests shared by test_str, test_unicode, test_userstring and test_string.
 import unittest, string, sys, struct
 from test import test_support
 from UserList import UserList
-import _testcapi
 
 class Sequence:
     def __init__(self, seq='wxyz'): self.seq = seq
@@ -1114,27 +1113,31 @@ class MixinStrUnicodeUserStringTest:
         self.checkraises(TypeError, '%10.*f', '__mod__', ('foo', 42.))
         self.checkraises(ValueError, '%10', '__mod__', (42,))
 
-        width = int(_testcapi.PY_SSIZE_T_MAX + 1)
+        class X(object): pass
+        self.checkraises(TypeError, 'abc', '__mod__', X())
+        class X(Exception):
+            def __getitem__(self, k):
+                return k
+        self.checkequal('melon apple', '%(melon)s %(apple)s', '__mod__', X())
+
+    @test_support.cpython_only
+    def test_formatting_c_limits(self):
+        from _testcapi import PY_SSIZE_T_MAX, INT_MAX, UINT_MAX
+        SIZE_MAX = (1 << (PY_SSIZE_T_MAX.bit_length() + 1)) - 1
+        width = int(PY_SSIZE_T_MAX + 1)
         if width <= sys.maxint:
             self.checkraises(OverflowError, '%*s', '__mod__', (width, ''))
-        prec = int(_testcapi.INT_MAX + 1)
+        prec = int(INT_MAX + 1)
         if prec <= sys.maxint:
             self.checkraises(OverflowError, '%.*f', '__mod__', (prec, 1. / 7))
         # Issue 15989
-        width = int(1 << (_testcapi.PY_SSIZE_T_MAX.bit_length() + 1))
+        width = int(SIZE_MAX + 1)
         if width <= sys.maxint:
             self.checkraises(OverflowError, '%*s', '__mod__', (width, ''))
-        prec = int(_testcapi.UINT_MAX + 1)
+        prec = int(UINT_MAX + 1)
         if prec <= sys.maxint:
             self.checkraises(OverflowError, '%.*f', '__mod__', (prec, 1. / 7))
 
-        class X(object): pass
-        self.checkraises(TypeError, 'abc', '__mod__', X())
-        class X(Exception):
-            def __getitem__(self, k):
-                return k
-        self.checkequal('melon apple', '%(melon)s %(apple)s', '__mod__', X())
-
     def test_floatformatting(self):
         # float formatting
         for prec in xrange(100):
diff --git a/Lib/test/test_capi.py b/Lib/test/test_capi.py
index 0edb3bf..a2cb5c7 100644
--- a/Lib/test/test_capi.py
+++ b/Lib/test/test_capi.py
@@ -13,7 +13,9 @@ try:
 except ImportError:
     thread = None
     threading = None
-import _testcapi
+# Skip this test if the _testcapi module isn't available.
+_testcapi = test_support.import_module('_testcapi')
+
 
 @unittest.skipUnless(threading, 'Threading required for this test.')
 class TestPendingCalls(unittest.TestCase):
diff --git a/Lib/test/test_code.py b/Lib/test/test_code.py
index 97adf59..c588999 100644
--- a/Lib/test/test_code.py
+++ b/Lib/test/test_code.py
@@ -82,7 +82,7 @@ consts: ("'doc string'", 'None')
 
 import unittest
 import weakref
-import _testcapi
+from test.test_support import run_doctest, run_unittest, cpython_only
 
 
 def consts(t):
@@ -104,7 +104,9 @@ def dump(co):
 
 class CodeTest(unittest.TestCase):
 
+    @cpython_only
     def test_newempty(self):
+        import _testcapi
         co = _testcapi.code_newempty("filename", "funcname", 15)
         self.assertEqual(co.co_filename, "filename")
         self.assertEqual(co.co_name, "funcname")
@@ -137,7 +139,6 @@ class CodeWeakRefTest(unittest.TestCase):
 
 
 def test_main(verbose=None):
-    from test.test_support import run_doctest, run_unittest
     from test import test_code
     run_doctest(test_code, verbose)
     run_unittest(CodeTest, CodeWeakRefTest)
diff --git a/Lib/test/test_codecs.py b/Lib/test/test_codecs.py
index 7a4c70b..f2ec670 100644
--- a/Lib/test/test_codecs.py
+++ b/Lib/test/test_codecs.py
@@ -2,7 +2,7 @@ from test import test_support
 import unittest
 import codecs
 import locale
-import sys, StringIO, _testcapi
+import sys, StringIO
 
 def coding_checker(self, coder):
     def check(input, expect):
@@ -1539,7 +1539,7 @@ else:
 
 class BasicUnicodeTest(unittest.TestCase):
     def test_basics(self):
-        s = u"abc123" # all codecs should be able to encode these
+        s = u"abc123"  # all codecs should be able to encode these
         for encoding in all_unicode_encodings:
             name = codecs.lookup(encoding).name
             if encoding.endswith("_codec"):
@@ -1548,9 +1548,9 @@ class BasicUnicodeTest(unittest.TestCase):
                 name = "latin_1"
             self.assertEqual(encoding.replace("_", "-"), name.replace("_", "-"))
             (bytes, size) = codecs.getencoder(encoding)(s)
-            self.assertEqual(size, len(s), "%r != %r (encoding=%r)" % (size, len(s), encoding))
+            self.assertEqual(size, len(s), "encoding=%r" % encoding)
             (chars, size) = codecs.getdecoder(encoding)(bytes)
-            self.assertEqual(chars, s, "%r != %r (encoding=%r)" % (chars, s, encoding))
+            self.assertEqual(chars, s, "encoding=%r" % encoding)
 
             if encoding not in broken_unicode_with_streams:
                 # check stream reader/writer
@@ -1566,15 +1566,13 @@ class BasicUnicodeTest(unittest.TestCase):
                 for c in encodedresult:
                     q.write(c)
                     decodedresult += reader.read()
-                self.assertEqual(decodedresult, s, "%r != %r (encoding=%r)" % (decodedresult, s, encoding))
+                self.assertEqual(decodedresult, s, "encoding=%r" % encoding)
 
             if encoding not in broken_incremental_coders:
-                # check incremental decoder/encoder (fetched via the Python
-                # and C API) and iterencode()/iterdecode()
+                # check incremental decoder/encoder and iterencode()/iterdecode()
                 try:
                     encoder = codecs.getincrementalencoder(encoding)()
-                    cencoder = _testcapi.codec_incrementalencoder(encoding)
-                except LookupError: # no IncrementalEncoder
+                except LookupError:  # no IncrementalEncoder
                     pass
                 else:
                     # check incremental decoder/encoder
@@ -1587,45 +1585,71 @@ class BasicUnicodeTest(unittest.TestCase):
                     for c in encodedresult:
                         decodedresult += decoder.decode(c)
                     decodedresult += decoder.decode("", True)
-                    self.assertEqual(decodedresult, s, "%r != %r (encoding=%r)" % (decodedresult, s, encoding))
+                    self.assertEqual(decodedresult, s,
+                                     "encoding=%r" % encoding)
+
+                    # check iterencode()/iterdecode()
+                    result = u"".join(codecs.iterdecode(
+                            codecs.iterencode(s, encoding), encoding))
+                    self.assertEqual(result, s, "encoding=%r" % encoding)
 
+                    # check iterencode()/iterdecode() with empty string
+                    result = u"".join(codecs.iterdecode(
+                            codecs.iterencode(u"", encoding), encoding))
+                    self.assertEqual(result, u"")
+
+                if encoding not in only_strict_mode:
+                    # check incremental decoder/encoder with errors argument
+                    try:
+                        encoder = codecs.getincrementalencoder(encoding)("ignore")
+                    except LookupError:  # no IncrementalEncoder
+                        pass
+                    else:
+                        encodedresult = "".join(encoder.encode(c) for c in s)
+                        decoder = codecs.getincrementaldecoder(encoding)("ignore")
+                        decodedresult = u"".join(decoder.decode(c)
+                                                 for c in encodedresult)
+                        self.assertEqual(decodedresult, s,
+                                         "encoding=%r" % encoding)
+
+    @test_support.cpython_only
+    def test_basics_capi(self):
+        from _testcapi import codec_incrementalencoder, codec_incrementaldecoder
+        s = u"abc123"  # all codecs should be able to encode these
+        for encoding in all_unicode_encodings:
+            if encoding not in broken_incremental_coders:
+                # check incremental decoder/encoder and iterencode()/iterdecode()
+                try:
+                    cencoder = codec_incrementalencoder(encoding)
+                except LookupError:  # no IncrementalEncoder
+                    pass
+                else:
                     # check C API
                     encodedresult = ""
                     for c in s:
                         encodedresult += cencoder.encode(c)
                     encodedresult += cencoder.encode(u"", True)
-                    cdecoder = _testcapi.codec_incrementaldecoder(encoding)
+                    cdecoder = codec_incrementaldecoder(encoding)
                     decodedresult = u""
                     for c in encodedresult:
                         decodedresult += cdecoder.decode(c)
                     decodedresult += cdecoder.decode("", True)
-                    self.assertEqual(decodedresult, s, "%r != %r (encoding=%r)" % (decodedresult, s, encoding))
-
-                    # check iterencode()/iterdecode()
-                    result = u"".join(codecs.iterdecode(codecs.iterencode(s, encoding), encoding))
-                    self.assertEqual(result, s, "%r != %r (encoding=%r)" % (result, s, encoding))
-
-                    # check iterencode()/iterdecode() with empty string
-                    result = u"".join(codecs.iterdecode(codecs.iterencode(u"", encoding), encoding))
-                    self.assertEqual(result, u"")
+                    self.assertEqual(decodedresult, s,
+                                     "encoding=%r" % encoding)
 
                 if encoding not in only_strict_mode:
                     # check incremental decoder/encoder with errors argument
                     try:
-                        encoder = codecs.getincrementalencoder(encoding)("ignore")
-                        cencoder = _testcapi.codec_incrementalencoder(encoding, "ignore")
-                    except LookupError: # no IncrementalEncoder
+                        cencoder = codec_incrementalencoder(encoding, "ignore")
+                    except LookupError:  # no IncrementalEncoder
                         pass
                     else:
-                        encodedresult = "".join(encoder.encode(c) for c in s)
-                        decoder = codecs.getincrementaldecoder(encoding)("ignore")
-                        decodedresult = u"".join(decoder.decode(c) for c in encodedresult)
-                        self.assertEqual(decodedresult, s, "%r != %r (encoding=%r)" % (decodedresult, s, encoding))
-
                         encodedresult = "".join(cencoder.encode(c) for c in s)
-                        cdecoder = _testcapi.codec_incrementaldecoder(encoding, "ignore")
-                        decodedresult = u"".join(cdecoder.decode(c) for c in encodedresult)
-                        self.assertEqual(decodedresult, s, "%r != %r (encoding=%r)" % (decodedresult, s, encoding))
+                        cdecoder = codec_incrementaldecoder(encoding, "ignore")
+                        decodedresult = u"".join(cdecoder.decode(c)
+                                                 for c in encodedresult)
+                        self.assertEqual(decodedresult, s,
+                                         "encoding=%r" % encoding)
 
     def test_seek(self):
         # all codecs should be able to encode these
diff --git a/Lib/test/test_descr.py b/Lib/test/test_descr.py
index 15a3049..6f91842 100644
--- a/Lib/test/test_descr.py
+++ b/Lib/test/test_descr.py
@@ -2092,6 +2092,7 @@ order (MRO) for bases """
             prop2 = property(fset=setter)
             self.assertEqual(prop2.__doc__, None)
 
+    @test_support.cpython_only
     def test_testcapi_no_segfault(self):
         # this segfaulted in 2.5b2
         try:
diff --git a/Lib/test/test_fcntl.py b/Lib/test/test_fcntl.py
index a45140f..3a18031 100644
--- a/Lib/test/test_fcntl.py
+++ b/Lib/test/test_fcntl.py
@@ -6,10 +6,9 @@ OS/2+EMX doesn't support the file locking operations.
 import os
 import struct
 import sys
-import _testcapi
 import unittest
 from test.test_support import (verbose, TESTFN, unlink, run_unittest,
-    import_module)
+    import_module, cpython_only)
 
 # Skip test if no fcntl module.
 fcntl = import_module('fcntl')
@@ -52,6 +51,12 @@ def get_lockdata():
 lockdata = get_lockdata()
 
 
+class BadFile:
+    def __init__(self, fn):
+        self.fn = fn
+    def fileno(self):
+        return self.fn
+
 class TestFcntl(unittest.TestCase):
 
     def setUp(self):
@@ -83,24 +88,27 @@ class TestFcntl(unittest.TestCase):
         self.f.close()
 
     def test_fcntl_bad_file(self):
-        class F:
-            def __init__(self, fn):
-                self.fn = fn
-            def fileno(self):
-                return self.fn
-        self.assertRaises(ValueError, fcntl.fcntl, -1, fcntl.F_SETFL, os.O_NONBLOCK)
-        self.assertRaises(ValueError, fcntl.fcntl, F(-1), fcntl.F_SETFL, os.O_NONBLOCK)
-        self.assertRaises(TypeError, fcntl.fcntl, 'spam', fcntl.F_SETFL, os.O_NONBLOCK)
-        self.assertRaises(TypeError, fcntl.fcntl, F('spam'), fcntl.F_SETFL, os.O_NONBLOCK)
+        with self.assertRaises(ValueError):
+            fcntl.fcntl(-1, fcntl.F_SETFL, os.O_NONBLOCK)
+        with self.assertRaises(ValueError):
+            fcntl.fcntl(BadFile(-1), fcntl.F_SETFL, os.O_NONBLOCK)
+        with self.assertRaises(TypeError):
+            fcntl.fcntl('spam', fcntl.F_SETFL, os.O_NONBLOCK)
+        with self.assertRaises(TypeError):
+            fcntl.fcntl(BadFile('spam'), fcntl.F_SETFL, os.O_NONBLOCK)
+
+    @cpython_only
+    def test_fcntl_bad_file_overflow(self):
+        from _testcapi import INT_MAX, INT_MIN
         # Issue 15989
-        self.assertRaises(ValueError, fcntl.fcntl, _testcapi.INT_MAX + 1,
-                                                   fcntl.F_SETFL, os.O_NONBLOCK)
-        self.assertRaises(ValueError, fcntl.fcntl, F(_testcapi.INT_MAX + 1),
-                                                   fcntl.F_SETFL, os.O_NONBLOCK)
-        self.assertRaises(ValueError, fcntl.fcntl, _testcapi.INT_MIN - 1,
-                                                   fcntl.F_SETFL, os.O_NONBLOCK)
-        self.assertRaises(ValueError, fcntl.fcntl, F(_testcapi.INT_MIN - 1),
-                                                   fcntl.F_SETFL, os.O_NONBLOCK)
+        with self.assertRaises(ValueError):
+            fcntl.fcntl(INT_MAX + 1, fcntl.F_SETFL, os.O_NONBLOCK)
+        with self.assertRaises(ValueError):
+            fcntl.fcntl(BadFile(INT_MAX + 1), fcntl.F_SETFL, os.O_NONBLOCK)
+        with self.assertRaises(ValueError):
+            fcntl.fcntl(INT_MIN - 1, fcntl.F_SETFL, os.O_NONBLOCK)
+        with self.assertRaises(ValueError):
+            fcntl.fcntl(BadFile(INT_MIN - 1), fcntl.F_SETFL, os.O_NONBLOCK)
 
     def test_fcntl_64_bit(self):
         # Issue #1309352: fcntl shouldn't fail when the third arg fits in a
diff --git a/Lib/test/test_fileio.py b/Lib/test/test_fileio.py
index c2a63ad..b45d79b 100644
--- a/Lib/test/test_fileio.py
+++ b/Lib/test/test_fileio.py
@@ -10,10 +10,9 @@ from array import array
 from weakref import proxy
 from functools import wraps
 from UserList import UserList
-import _testcapi
 
 from test.test_support import TESTFN, check_warnings, run_unittest, make_bad_fd
-from test.test_support import py3k_bytes as bytes
+from test.test_support import py3k_bytes as bytes, cpython_only
 from test.script_helper import run_python
 
 from _io import FileIO as _FileIO
@@ -359,7 +358,11 @@ class OtherFileTests(unittest.TestCase):
         if sys.platform == 'win32':
             import msvcrt
             self.assertRaises(IOError, msvcrt.get_osfhandle, make_bad_fd())
+
+    @cpython_only
+    def testInvalidFd_overflow(self):
         # Issue 15989
+        import _testcapi
         self.assertRaises(TypeError, _FileIO, _testcapi.INT_MAX + 1)
         self.assertRaises(TypeError, _FileIO, _testcapi.INT_MIN - 1)
 
diff --git a/Lib/test/test_format.py b/Lib/test/test_format.py
index 0ad8b02..ba3399e 100644
--- a/Lib/test/test_format.py
+++ b/Lib/test/test_format.py
@@ -303,22 +303,32 @@ def test_main():
     test_support.run_unittest(FormatTest)
 
     def test_precision(self):
-        INT_MAX = 2147483647
-
         f = 1.2
         self.assertEqual(format(f, ".0f"), "1")
         self.assertEqual(format(f, ".3f"), "1.200")
         with self.assertRaises(ValueError) as cm:
-            format(f, ".%sf" % (INT_MAX + 1))
+            format(f, ".%sf" % (sys.maxsize + 1))
         self.assertEqual(str(cm.exception), "precision too big")
 
         c = complex(f)
-        self.assertEqual(format(f, ".0f"), "1")
-        self.assertEqual(format(f, ".3f"), "1.200")
+        self.assertEqual(format(c, ".0f"), "1+0j")
+        self.assertEqual(format(c, ".3f"), "1.200+0.000j")
         with self.assertRaises(ValueError) as cm:
-            format(f, ".%sf" % (INT_MAX + 1))
+            format(c, ".%sf" % (sys.maxsize + 1))
         self.assertEqual(str(cm.exception), "precision too big")
 
+    @test_support.cpython_only
+    def test_precision_c_limits(self):
+        from _testcapi import INT_MAX
+
+        f = 1.2
+        with self.assertRaises(ValueError) as cm:
+            format(f, ".%sf" % (INT_MAX + 1))
+
+        c = complex(f)
+        with self.assertRaises(ValueError) as cm:
+            format(c, ".%sf" % (INT_MAX + 1))
+
 
 if __name__ == "__main__":
     unittest.main()
diff --git a/Lib/test/test_getargs2.py b/Lib/test/test_getargs2.py
index 07d97c1..aba304a 100644
--- a/Lib/test/test_getargs2.py
+++ b/Lib/test/test_getargs2.py
@@ -1,5 +1,7 @@
 import unittest
 from test import test_support
+# Skip this test if the _testcapi module isn't available.
+test_support.import_module('_testcapi')
 from _testcapi import getargs_keywords
 import warnings
 
diff --git a/Lib/test/test_poll.py b/Lib/test/test_poll.py
index e4cdc16..1e195ed 100644
--- a/Lib/test/test_poll.py
+++ b/Lib/test/test_poll.py
@@ -3,14 +3,13 @@
 import os
 import random
 import select
-from _testcapi import USHRT_MAX, INT_MAX, UINT_MAX
 try:
     import threading
 except ImportError:
     threading = None
 import time
 import unittest
-from test.test_support import TESTFN, run_unittest, reap_threads
+from test.test_support import TESTFN, run_unittest, reap_threads, cpython_only
 
 try:
     select.poll
@@ -161,8 +160,18 @@ class PollTests(unittest.TestCase):
 
         # Issues #15989, #17919
         self.assertRaises(OverflowError, pollster.register, 0, -1)
-        self.assertRaises(OverflowError, pollster.register, 0, USHRT_MAX + 1)
+        self.assertRaises(OverflowError, pollster.register, 0, 1 << 64)
         self.assertRaises(OverflowError, pollster.modify, 1, -1)
+        self.assertRaises(OverflowError, pollster.modify, 1, 1 << 64)
+
+    @cpython_only
+    def test_poll_c_limits(self):
+        from _testcapi import USHRT_MAX, INT_MAX, UINT_MAX
+        pollster = select.poll()
+        pollster.register(1)
+
+        # Issues #15989, #17919
+        self.assertRaises(OverflowError, pollster.register, 0, USHRT_MAX + 1)
         self.assertRaises(OverflowError, pollster.modify, 1, USHRT_MAX + 1)
         self.assertRaises(OverflowError, pollster.poll, INT_MAX + 1)
         self.assertRaises(OverflowError, pollster.poll, UINT_MAX + 1)
diff --git a/Lib/test/test_socket.py b/Lib/test/test_socket.py
index 35e983e..5fd96fe 100644
--- a/Lib/test/test_socket.py
+++ b/Lib/test/test_socket.py
@@ -4,7 +4,6 @@ from test import test_support
 import errno
 import socket
 import select
-import _testcapi
 import time
 import traceback
 import Queue
@@ -711,7 +710,10 @@ class GeneralModuleTests(unittest.TestCase):
             srv.listen(backlog)
             srv.close()
 
+    @test_support.cpython_only
+    def test_listen_backlog_overflow(self):
         # Issue 15989
+        import _testcapi
         srv = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
         srv.bind((HOST, 0))
         self.assertRaises(OverflowError, srv.listen, _testcapi.INT_MAX + 1)
@@ -818,6 +820,14 @@ class BasicTCPTest(SocketConnectedTest):
 
     def _testShutdown(self):
         self.serv_conn.send(MSG)
+        self.serv_conn.shutdown(2)
+
+    testShutdown_overflow = test_support.cpython_only(testShutdown)
+
+    @test_support.cpython_only
+    def _testShutdown_overflow(self):
+        import _testcapi
+        self.serv_conn.send(MSG)
         # Issue 15989
         self.assertRaises(OverflowError, self.serv_conn.shutdown,
                           _testcapi.INT_MAX + 1)
@@ -911,14 +921,23 @@ class NonBlockingTCPTests(ThreadedTCPSocketTest):
             pass
         end = time.time()
         self.assertTrue((end - start) < 1.0, "Error setting non-blocking mode.")
-        # Issue 15989
-        if _testcapi.UINT_MAX < _testcapi.ULONG_MAX:
-            self.serv.setblocking(_testcapi.UINT_MAX + 1)
-            self.assertIsNone(self.serv.gettimeout())
 
     def _testSetBlocking(self):
         pass
 
+    @test_support.cpython_only
+    def testSetBlocking_overflow(self):
+        # Issue 15989
+        import _testcapi
+        if _testcapi.UINT_MAX >= _testcapi.ULONG_MAX:
+            self.skipTest('needs UINT_MAX < ULONG_MAX')
+        self.serv.setblocking(False)
+        self.assertEqual(self.serv.gettimeout(), 0.0)
+        self.serv.setblocking(_testcapi.UINT_MAX + 1)
+        self.assertIsNone(self.serv.gettimeout())
+
+    _testSetBlocking_overflow = test_support.cpython_only(_testSetBlocking)
+
     def testAccept(self):
         # Testing non-blocking accept
         self.serv.setblocking(0)
diff --git a/Lib/test/test_structmembers.py b/Lib/test/test_structmembers.py
index 0cc58c3..3e2b261 100644
--- a/Lib/test/test_structmembers.py
+++ b/Lib/test/test_structmembers.py
@@ -1,3 +1,8 @@
+import unittest
+from test import test_support
+
+# Skip this test if the _testcapi module isn't available.
+test_support.import_module('_testcapi')
 from _testcapi import _test_structmembersType, \
     CHAR_MAX, CHAR_MIN, UCHAR_MAX, \
     SHRT_MAX, SHRT_MIN, USHRT_MAX, \
@@ -5,9 +10,6 @@ from _testcapi import _test_structmembersType, \
     LONG_MAX, LONG_MIN, ULONG_MAX, \
     LLONG_MAX, LLONG_MIN, ULLONG_MAX
 
-import unittest
-from test import test_support
-
 ts=_test_structmembersType(False, 1, 2, 3, 4, 5, 6, 7, 8,
                           9.99999, 10.1010101010, "hi")
 
diff --git a/Lib/test/test_support.py b/Lib/test/test_support.py
index d82edb0..a40a593 100644
--- a/Lib/test/test_support.py
+++ b/Lib/test/test_support.py
@@ -19,7 +19,6 @@ import UserDict
 import re
 import time
 import struct
-import _testcapi
 import sysconfig
 try:
     import thread
@@ -1002,6 +1001,7 @@ _TPFLAGS_HAVE_GC = 1<<14
 _TPFLAGS_HEAPTYPE = 1<<9
 
 def check_sizeof(test, o, size):
+    import _testcapi
     result = sys.getsizeof(o)
     # add GC header size
     if ((type(o) == type) and (o.__flags__ & _TPFLAGS_HEAPTYPE) or\
diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py
index fcca676..7277547 100644
--- a/Lib/test/test_sys.py
+++ b/Lib/test/test_sys.py
@@ -489,6 +489,7 @@ class SysModuleTest(unittest.TestCase):
         p.wait()
         self.assertIn(executable, ["''", repr(sys.executable)])
 
+@test.test_support.cpython_only
 class SizeofTest(unittest.TestCase):
 
     def setUp(self):
diff --git a/Lib/test/test_tcl.py b/Lib/test/test_tcl.py
index 49bca96..a6e95e5 100644
--- a/Lib/test/test_tcl.py
+++ b/Lib/test/test_tcl.py
@@ -1,7 +1,6 @@
 import unittest
 import sys
 import os
-import _testcapi
 from test import test_support
 from subprocess import Popen, PIPE
 
@@ -11,6 +10,11 @@ _tkinter = test_support.import_module('_tkinter')
 from Tkinter import Tcl
 from _tkinter import TclError
 
+try:
+    from _testcapi import INT_MAX, PY_SSIZE_T_MAX
+except ImportError:
+    INT_MAX = PY_SSIZE_T_MAX = sys.maxsize
+
 tcl_version = _tkinter.TCL_VERSION.split('.')
 try:
     for i in range(len(tcl_version)):
@@ -523,10 +527,9 @@ class BigmemTclTest(unittest.TestCase):
     def setUp(self):
         self.interp = Tcl()
 
-    @unittest.skipUnless(_testcapi.INT_MAX < _testcapi.PY_SSIZE_T_MAX,
-                         "needs UINT_MAX < SIZE_MAX")
-    @test_support.precisionbigmemtest(size=_testcapi.INT_MAX + 1, memuse=5,
-                                      dry_run=False)
+    @test_support.cpython_only
+    @unittest.skipUnless(INT_MAX < PY_SSIZE_T_MAX, "needs UINT_MAX < SIZE_MAX")
+    @test_support.precisionbigmemtest(size=INT_MAX + 1, memuse=5, dry_run=False)
     def test_huge_string(self, size):
         value = ' ' * size
         self.assertRaises(OverflowError, self.interp.call, 'set', '_', value)
diff --git a/Lib/test/test_threading.py b/Lib/test/test_threading.py
index 41be68e..1653d36 100644
--- a/Lib/test/test_threading.py
+++ b/Lib/test/test_threading.py
@@ -1,7 +1,7 @@
 # Very rudimentary test of threading module
 
 import test.test_support
-from test.test_support import verbose
+from test.test_support import verbose, cpython_only
 from test.script_helper import assert_python_ok
 
 import random
@@ -724,6 +724,7 @@ class ThreadJoinOnShutdown(BaseTestCase):
         for t in threads:
             t.join()
 
+    @cpython_only
     @unittest.skipIf(_testcapi is None, "need _testcapi module")
     def test_frame_tstate_tracing(self):
         # Issue #14432: Crash when a generator is created in a C thread that is
diff --git a/Lib/test/test_traceback.py b/Lib/test/test_traceback.py
index d7b183a..8b0322b 100644
--- a/Lib/test/test_traceback.py
+++ b/Lib/test/test_traceback.py
@@ -1,11 +1,10 @@
 """Test cases for traceback module"""
 
-from _testcapi import traceback_print
 from StringIO import StringIO
 import sys
 import unittest
 from imp import reload
-from test.test_support import run_unittest, is_jython, Error
+from test.test_support import run_unittest, is_jython, Error, cpython_only
 
 import traceback
 
@@ -181,7 +180,9 @@ def test():
 
 class TracebackFormatTests(unittest.TestCase):
 
+    @cpython_only
     def test_traceback_format(self):
+        from _testcapi import traceback_print
         try:
             raise KeyError('blah')
         except KeyError:
diff --git a/Lib/test/test_ucn.py b/Lib/test/test_ucn.py
index cba4f07..4409deb 100644
--- a/Lib/test/test_ucn.py
+++ b/Lib/test/test_ucn.py
@@ -9,10 +9,14 @@ Modified for Python 2.0 by Fredrik Lundh (fredrik@pythonware.com)
 
 import unittest
 import sys
-import _testcapi
 
 from test import test_support
 
+try:
+    from _testcapi import INT_MAX, PY_SSIZE_T_MAX, UINT_MAX
+except ImportError:
+    INT_MAX = PY_SSIZE_T_MAX = UINT_MAX = 2**64 - 1
+
 class UnicodeNamesTest(unittest.TestCase):
 
     def checkletter(self, name, code):
@@ -139,11 +143,10 @@ class UnicodeNamesTest(unittest.TestCase):
             unicode, "\\NSPACE", 'unicode-escape', 'strict'
         )
 
-    @unittest.skipUnless(_testcapi.INT_MAX < _testcapi.PY_SSIZE_T_MAX,
-                         "needs UINT_MAX < SIZE_MAX")
-    @unittest.skipUnless(_testcapi.UINT_MAX < sys.maxint,
-                         "needs UINT_MAX < sys.maxint")
-    @test_support.bigmemtest(minsize=_testcapi.UINT_MAX + 1,
+    @test_support.cpython_only
+    @unittest.skipUnless(INT_MAX < PY_SSIZE_T_MAX, "needs UINT_MAX < SIZE_MAX")
+    @unittest.skipUnless(UINT_MAX < sys.maxint, "needs UINT_MAX < sys.maxint")
+    @test_support.bigmemtest(minsize=UINT_MAX + 1,
                              memuse=2 + 4 // len(u'\U00010000'))
     def test_issue16335(self, size):
         func = self.test_issue16335
@@ -151,9 +154,8 @@ class UnicodeNamesTest(unittest.TestCase):
             raise unittest.SkipTest("not enough memory: %.1fG minimum needed" %
                     (func.minsize * func.memuse / float(1024**3),))
         # very very long bogus character name
-        x = b'\\N{SPACE' + b'x' * int(_testcapi.UINT_MAX + 1) + b'}'
-        self.assertEqual(len(x), len(b'\\N{SPACE}') +
-                                    (_testcapi.UINT_MAX + 1))
+        x = b'\\N{SPACE' + b'x' * int(UINT_MAX + 1) + b'}'
+        self.assertEqual(len(x), len(b'\\N{SPACE}') + (UINT_MAX + 1))
         self.assertRaisesRegexp(UnicodeError,
             'unknown Unicode character name',
             x.decode, 'unicode-escape'
diff --git a/Lib/test/test_unicode.py b/Lib/test/test_unicode.py
index cbdaddd..da176b8 100644
--- a/Lib/test/test_unicode.py
+++ b/Lib/test/test_unicode.py
@@ -644,8 +644,13 @@ class UnicodeTest(
                 return u'\u1234'
         self.assertEqual('%s' % Wrapper(), u'\u1234')
 
-    @test_support.cpython_only
     def test_formatting_huge_precision(self):
+        format_string = u"%.{}f".format(sys.maxsize + 1)
+        with self.assertRaises(ValueError):
+            result = format_string % 2.34
+
+    @test_support.cpython_only
+    def test_formatting_huge_precision_c_limits(self):
         from _testcapi import INT_MAX
         format_string = u"%.{}f".format(INT_MAX + 1)
         with self.assertRaises(ValueError):
@@ -1633,6 +1638,7 @@ class UnicodeTest(
         self.assertEqual("%s" % u, u'__unicode__ overridden')
         self.assertEqual("{}".format(u), '__unicode__ overridden')
 
+    @test_support.cpython_only
     def test_encode_decimal(self):
         from _testcapi import unicode_encodedecimal
         self.assertEqual(unicode_encodedecimal(u'123'),
@@ -1658,6 +1664,7 @@ class UnicodeTest(
         self.assertEqual(unicode_encodedecimal(u"123\u20ac\u0660", "replace"),
                          b'123?0')
 
+    @test_support.cpython_only
     def test_encode_decimal_with_surrogates(self):
         from _testcapi import unicode_encodedecimal
         tests = [(u'\U0001f49d', '&#128157;'),
diff --git a/Misc/NEWS b/Misc/NEWS
index 51e5d95..9520fa4 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -224,6 +224,8 @@ IDLE
 Tests
 -----
 
+- Issue #20532: Tests which use _testcapi now are marked as CPython only.
+
 - Issue #19920: Added tests for TarFile.list().  Based on patch by Vajrasky Kok.
 
 - Issue #19990: Added tests for the imghdr module.  Based on patch by