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).

1 files changed, 6 insertions, 1 deletions

diff --git a/Lib/test/test_doctest.py b/Lib/test/test_doctest.py
index 407a14c..8616aed 100644
--- a/Lib/test/test_doctest.py
+++ b/Lib/test/test_doctest.py
@@ -18,6 +18,11 @@ import shutil
 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 @@ We'll simulate a __file__ attr that ends in pyc:
     >>> 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.