bpo-40280: Skip socket, fork, subprocess tests on Emscripten (GH-31986)

- Add requires_fork and requires_subprocess to more tests
- Skip extension import tests if dlopen is not available
- Don't assume that _testcapi is a shared extension
- Skip a lot of socket tests that don't work on Emscripten
- Skip mmap tests, mmap emulation is incomplete
- venv does not work yet
- Cannot get libc from executable

The "entire" test suite is now passing on Emscripten with EMSDK from git head (91 suites are skipped).

Author: tiran

Lib/test/lock_tests.py

@@ -15,7 +15,7 @@
 from test.support import threading_helper
 
 
-requires_fork = unittest.skipUnless(hasattr(os, 'fork'),
+requires_fork = unittest.skipUnless(support.has_fork_support,
                                     "platform doesn't support fork "
                                      "(no _at_fork_reinit method)")
 

Lib/test/pythoninfo.py

@@ -6,6 +6,7 @@
 import re
 import sys
 import traceback
+import unittest
 import warnings
 
 
@@ -615,7 +616,7 @@ def collect_resource(info_add):
 def collect_test_socket(info_add):
     try:
         from test import test_socket
-    except ImportError:
+    except (ImportError, unittest.SkipTest):
         return
 
     # all check attributes like HAVE_SOCKET_CAN

Lib/test/support/__init__.py

@@ -42,6 +42,7 @@
     "requires_IEEE_754", "requires_zlib",
     "has_fork_support", "requires_fork",
     "has_subprocess_support", "requires_subprocess",
+    "has_socket_support", "requires_working_socket",
     "anticipate_failure", "load_package_tests", "detect_api_mismatch",
     "check__all__", "skip_if_buggy_ucrt_strfptime",
     "check_disallow_instantiation", "check_sanitizer", "skip_if_sanitizer",
@@ -520,6 +521,21 @@ def requires_subprocess():
     """Used for subprocess, os.spawn calls, fd inheritance"""
     return unittest.skipUnless(has_subprocess_support, "requires subprocess support")
 
+# Emscripten's socket emulation has limitation. WASI doesn't have sockets yet.
+has_socket_support = not is_emscripten and not is_wasi
+
+def requires_working_socket(*, module=False):
+    """Skip tests or modules that require working sockets
+
+    Can be used as a function/class decorator or to skip an entire module.
+    """
+    msg = "requires socket support"
+    if module:
+        if not has_socket_support:
+            raise unittest.SkipTest(msg)
+    else:
+        return unittest.skipUnless(has_socket_support, msg)
+
 # Does strftime() support glibc extension like '%4Y'?
 has_strftime_extensions = False
 if sys.platform != "win32":

Lib/test/test_asyncgen.py

@@ -4,10 +4,12 @@
 import contextlib
 
 from test.support.import_helper import import_module
-from test.support import gc_collect
+from test.support import gc_collect, requires_working_socket
 asyncio = import_module("asyncio")
 
 
+requires_working_socket(module=True)
+
 _no_default = object()
 
 

Lib/test/test_asynchat.py

@@ -18,6 +18,8 @@
     import asynchat
     import asyncore
 
+support.requires_working_socket(module=True)
+
 HOST = socket_helper.HOST
 SERVER_QUIT = b'QUIT\n'
 

Lib/test/test_asyncio/__init__.py

@@ -1,7 +1,9 @@
 import os
+from test import support
 from test.support import load_package_tests
 from test.support import import_helper
 
+support.requires_working_socket(module=True)
 
 # Skip tests if we don't have concurrent.futures.
 import_helper.import_module('concurrent.futures')

Lib/test/test_asyncore.py

@@ -18,6 +18,8 @@
 if support.PGO:
     raise unittest.SkipTest("test is not helpful for PGO")
 
+support.requires_working_socket(module=True)
+
 import warnings
 with warnings.catch_warnings():
     warnings.simplefilter('ignore', DeprecationWarning)

Lib/test/test_contextlib_async.py

@@ -8,6 +8,7 @@
 
 from test.test_contextlib import TestBaseExitStack
 
+support.requires_working_socket(module=True)
 
 def _async_test(func):
     """Decorator to turn an async function into a test case."""

Lib/test/test_doctest.py

@@ -18,6 +18,11 @@
 import types
 import contextlib
 
+
+if not support.has_subprocess_support:
+    raise unittest.SkipTest("test_CLI requires subprocess support.")
+
+
 # NOTE: There are some additional tests relating to interaction with
 #       zipimport in the test_zipimport_support test module.
 
@@ -455,7 +460,7 @@ def basics(): r"""
     >>> tests = finder.find(sample_func)
 
     >>> print(tests)  # doctest: +ELLIPSIS
-    [<DocTest sample_func from test_doctest.py:28 (1 example)>]
+    [<DocTest sample_func from test_doctest.py:33 (1 example)>]
 
 The exact name depends on how test_doctest was invoked, so allow for
 leading path components.

Lib/test/test_docxmlrpc.py

@@ -4,6 +4,9 @@
 import sys
 import threading
 import unittest
+from test import support
+
+support.requires_working_socket(module=True)
 
 def make_request_and_skipIf(condition, reason):
     # If we skip the test, we have to make a request because

Lib/test/test_ftplib.py

@@ -29,6 +29,7 @@
     import asyncore
     import asynchat
 
+support.requires_working_socket(module=True)
 
 TIMEOUT = support.LOOPBACK_TIMEOUT
 DEFAULT_ENCODING = 'utf-8'

Lib/test/test_httplib.py

@@ -19,6 +19,7 @@
 from test.support import socket_helper
 from test.support import warnings_helper
 
+support.requires_working_socket(module=True)
 
 here = os.path.dirname(__file__)
 # Self-signed cert file for 'localhost'

Lib/test/test_httpservers.py

@@ -33,6 +33,7 @@
 from test.support import os_helper
 from test.support import threading_helper
 
+support.requires_working_socket(module=True)
 
 class NoLogRequestHandler:
     def log_message(self, *args):

Lib/test/test_imaplib.py

@@ -11,7 +11,8 @@
 import socket
 
 from test.support import (verbose,
-                          run_with_tz, run_with_locale, cpython_only)
+                          run_with_tz, run_with_locale, cpython_only,
+                          requires_working_socket)
 from test.support import hashlib_helper
 from test.support import threading_helper
 from test.support import warnings_helper
@@ -23,6 +24,8 @@
 except ImportError:
     ssl = None
 
+support.requires_working_socket(module=True)
+
 CERTFILE = os.path.join(os.path.dirname(__file__) or os.curdir, "keycert3.pem")
 CAFILE = os.path.join(os.path.dirname(__file__) or os.curdir, "pycacert.pem")
 

Lib/test/test_import/__init__.py

@@ -20,7 +20,7 @@
 
 from test.support import os_helper
 from test.support import (
-    STDLIB_DIR, is_jython, swap_attr, swap_item, cpython_only)
+    STDLIB_DIR, is_jython, swap_attr, swap_item, cpython_only, is_emscripten)
 from test.support.import_helper import (
     forget, make_legacy_pyc, unlink, unload, DirsOnSysPath, CleanImport)
 from test.support.os_helper import (
@@ -101,8 +101,17 @@ def test_from_import_missing_attr_has_name_and_so_path(self):
         with self.assertRaises(ImportError) as cm:
             from _testcapi import i_dont_exist
         self.assertEqual(cm.exception.name, '_testcapi')
-        self.assertEqual(cm.exception.path, _testcapi.__file__)
-        self.assertRegex(str(cm.exception), r"cannot import name 'i_dont_exist' from '_testcapi' \(.*\.(so|pyd)\)")
+        if hasattr(_testcapi, "__file__"):
+            self.assertEqual(cm.exception.path, _testcapi.__file__)
+            self.assertRegex(
+                str(cm.exception),
+                r"cannot import name 'i_dont_exist' from '_testcapi' \(.*\.(so|pyd)\)"
+            )
+        else:
+            self.assertEqual(
+                str(cm.exception),
+                "cannot import name 'i_dont_exist' from '_testcapi' (unknown location)"
+            )
 
     def test_from_import_missing_attr_has_name(self):
         with self.assertRaises(ImportError) as cm:
@@ -525,6 +534,7 @@ class FilePermissionTests(unittest.TestCase):
 
     @unittest.skipUnless(os.name == 'posix',
                          "test meaningful only on posix systems")
+    @unittest.skipIf(is_emscripten, "Emscripten's umask is a stub.")
     def test_creation_mode(self):
         mask = 0o022
         with temp_umask(mask), _ready_to_import() as (name, path):

Lib/test/test_importlib/extension/test_finder.py

@@ -10,6 +10,10 @@ class FinderTests(abc.FinderTests):
 
     """Test the finder for extension modules."""
 
+    def setUp(self):
+        if not self.machinery.EXTENSION_SUFFIXES:
+            raise unittest.SkipTest("Requires dynamic loading support.")
+
     def find_spec(self, fullname):
         importer = self.machinery.FileFinder(util.EXTENSIONS.path,
                                             (self.machinery.ExtensionFileLoader,

Lib/test/test_importlib/extension/test_loader.py

@@ -12,11 +12,14 @@
 import importlib
 from test.support.script_helper import assert_python_failure
 
+
 class LoaderTests(abc.LoaderTests):
 
     """Test load_module() for extension modules."""
 
     def setUp(self):
+        if not self.machinery.EXTENSION_SUFFIXES:
+            raise unittest.SkipTest("Requires dynamic loading support.")
         self.loader = self.machinery.ExtensionFileLoader(util.EXTENSIONS.name,
                                                          util.EXTENSIONS.file_path)
 
@@ -91,6 +94,8 @@ class MultiPhaseExtensionModuleTests(abc.LoaderTests):
     # Test loading extension modules with multi-phase initialization (PEP 489).
 
     def setUp(self):
+        if not self.machinery.EXTENSION_SUFFIXES:
+            raise unittest.SkipTest("Requires dynamic loading support.")
         self.name = '_testmultiphase'
         finder = self.machinery.FileFinder(None)
         self.spec = importlib.util.find_spec(self.name)

Lib/test/test_json/test_tool.py

@@ -10,6 +10,7 @@
 from test.support.script_helper import assert_python_ok
 
 
+@support.requires_subprocess()
 class TestTool(unittest.TestCase):
     data = """
 

Lib/test/test_logging.py

@@ -75,6 +75,7 @@
 except ImportError:
     pass
 
+
 class BaseTest(unittest.TestCase):
 
     """Base class for logging tests."""
@@ -626,6 +627,9 @@ def test_path_objects(self):
             os.unlink(fn)
 
     @unittest.skipIf(os.name == 'nt', 'WatchedFileHandler not appropriate for Windows.')
+    @unittest.skipIf(
+        support.is_emscripten, "Emscripten cannot fstat unlinked files."
+    )
     def test_race(self):
         # Issue #14632 refers.
         def remove_loop(fname, tries):
@@ -1058,6 +1062,7 @@ class TestUnixDatagramServer(TestUDPServer):
 
 # - end of server_helper section
 
+@support.requires_working_socket()
 class SMTPHandlerTest(BaseTest):
     # bpo-14314, bpo-19665, bpo-34092: don't wait forever
     TIMEOUT = support.LONG_TIMEOUT
@@ -1681,6 +1686,7 @@ def test_defaults_do_no_interpolation(self):
             os.unlink(fn)
 
 
+@support.requires_working_socket()
 class SocketHandlerTest(BaseTest):
 
     """Test for SocketHandler objects."""
@@ -1795,6 +1801,7 @@ def tearDown(self):
         SocketHandlerTest.tearDown(self)
         os_helper.unlink(self.address)
 
+@support.requires_working_socket()
 class DatagramHandlerTest(BaseTest):
 
     """Test for DatagramHandler."""
@@ -1876,6 +1883,7 @@ def tearDown(self):
         DatagramHandlerTest.tearDown(self)
         os_helper.unlink(self.address)
 
+@support.requires_working_socket()
 class SysLogHandlerTest(BaseTest):
 
     """Test for SysLogHandler using UDP."""
@@ -1985,6 +1993,7 @@ def tearDown(self):
         self.server_class.address_family = socket.AF_INET
         super(IPv6SysLogHandlerTest, self).tearDown()
 
+@support.requires_working_socket()
 class HTTPHandlerTest(BaseTest):
     """Test for HTTPHandler."""
 
@@ -3261,6 +3270,7 @@ def setup_via_listener(self, text, verify=None):
             logging.config.stopListening()
             threading_helper.join_thread(t)
 
+    @support.requires_working_socket()
     def test_listen_config_10_ok(self):
         with support.captured_stdout() as output:
             self.setup_via_listener(json.dumps(self.config10))
@@ -3280,6 +3290,7 @@ def test_listen_config_10_ok(self):
                 ('ERROR', '4'),
             ], stream=output)
 
+    @support.requires_working_socket()
     def test_listen_config_1_ok(self):
         with support.captured_stdout() as output:
             self.setup_via_listener(textwrap.dedent(ConfigFileTest.config1))
@@ -3294,6 +3305,7 @@ def test_listen_config_1_ok(self):
             # Original logger output is empty.
             self.assert_log_lines([])
 
+    @support.requires_working_socket()
     def test_listen_verify(self):
 
         def verify_fail(stuff):

Lib/test/test_mailbox.py

@@ -1061,7 +1061,7 @@ def test_add_and_close(self):
             self.assertEqual(contents, f.read())
         self._box = self._factory(self._path)
 
-    @unittest.skipUnless(hasattr(os, 'fork'), "Test needs fork().")
+    @support.requires_fork()
     @unittest.skipUnless(hasattr(socket, 'socketpair'), "Test needs socketpair().")
     def test_lock_conflict(self):
         # Fork off a child process that will lock the mailbox temporarily,

Lib/test/test_mmap.py

@@ -1,4 +1,6 @@
-from test.support import (requires, _2G, _4G, gc_collect, cpython_only)
+from test.support import (
+    requires, _2G, _4G, gc_collect, cpython_only, is_emscripten
+)
 from test.support.import_helper import import_module
 from test.support.os_helper import TESTFN, unlink
 import unittest
@@ -21,6 +23,12 @@ def random_tagname(length=10):
     suffix = ''.join(random.choices(string.ascii_uppercase, k=length))
     return f'{tagname_prefix}_{suffix}'
 
+# Python's mmap module dup()s the file descriptor. Emscripten's FS layer
+# does not materialize file changes through a dupped fd to a new mmap.
+if is_emscripten:
+    raise unittest.SkipTest("incompatible with Emscripten's mmap emulation.")
+
+
 class MmapTests(unittest.TestCase):
 
     def setUp(self):

Lib/test/test_pdb.py

@@ -13,6 +13,7 @@
 
 from contextlib import ExitStack, redirect_stdout
 from io import StringIO
+from test import support
 from test.support import os_helper
 # This little helper class is essential for testing pdb under doctest.
 from test.test_doctest import _FakeInput
@@ -1363,6 +1364,7 @@ def test_pdb_issue_43318():
     """
 
 
+@support.requires_subprocess()
 class PdbTestCase(unittest.TestCase):
     def tearDown(self):
         os_helper.unlink(os_helper.TESTFN)

Lib/test/test_peg_generator/test_c_parser.py

@@ -70,6 +70,7 @@ def test_parse(self):
 """
 
 
+@support.requires_subprocess()
 class TestCParser(unittest.TestCase):
     def setUp(self):
         self._backup_config_vars = dict(sysconfig._CONFIG_VARS)