gh-76785: Show the Traceback for Uncaught Subinterpreter Exceptions (gh-113034)

When an exception is uncaught in Interpreter.exec_sync(), it helps to show that exception's error display if uncaught in the calling interpreter.  We do so here by generating a TracebackException in the subinterpreter and passing it between interpreters using pickle.

Lib/test/test_interpreters/utils.py

@@ -1,9 +1,16 @@
 import contextlib
 import os
+import os.path
+import subprocess
+import sys
+import tempfile
 import threading
 from textwrap import dedent
 import unittest
 
+from test import support
+from test.support import os_helper
+
 from test.support import interpreters
 
 
@@ -71,5 +78,70 @@ def ensure_closed(fd):
         self.addCleanup(lambda: ensure_closed(w))
         return r, w
 
+    def temp_dir(self):
+        tempdir = tempfile.mkdtemp()
+        tempdir = os.path.realpath(tempdir)
+        self.addCleanup(lambda: os_helper.rmtree(tempdir))
+        return tempdir
+
+    def make_script(self, filename, dirname=None, text=None):
+        if text:
+            text = dedent(text)
+        if dirname is None:
+            dirname = self.temp_dir()
+        filename = os.path.join(dirname, filename)
+
+        os.makedirs(os.path.dirname(filename), exist_ok=True)
+        with open(filename, 'w', encoding='utf-8') as outfile:
+            outfile.write(text or '')
+        return filename
+
+    def make_module(self, name, pathentry=None, text=None):
+        if text:
+            text = dedent(text)
+        if pathentry is None:
+            pathentry = self.temp_dir()
+        else:
+            os.makedirs(pathentry, exist_ok=True)
+        *subnames, basename = name.split('.')
+
+        dirname = pathentry
+        for subname in subnames:
+            dirname = os.path.join(dirname, subname)
+            if os.path.isdir(dirname):
+                pass
+            elif os.path.exists(dirname):
+                raise Exception(dirname)
+            else:
+                os.mkdir(dirname)
+            initfile = os.path.join(dirname, '__init__.py')
+            if not os.path.exists(initfile):
+                with open(initfile, 'w'):
+                    pass
+        filename = os.path.join(dirname, basename + '.py')
+
+        with open(filename, 'w', encoding='utf-8') as outfile:
+            outfile.write(text or '')
+        return filename
+
+    @support.requires_subprocess()
+    def run_python(self, *argv):
+        proc = subprocess.run(
+            [sys.executable, *argv],
+            capture_output=True,
+            text=True,
+        )
+        return proc.returncode, proc.stdout, proc.stderr
+
+    def assert_python_ok(self, *argv):
+        exitcode, stdout, stderr = self.run_python(*argv)
+        self.assertNotEqual(exitcode, 1)
+        return stdout, stderr
+
+    def assert_python_failure(self, *argv):
+        exitcode, stdout, stderr = self.run_python(*argv)
+        self.assertNotEqual(exitcode, 0)
+        return stdout, stderr
+
     def tearDown(self):
         clean_up_interpreters()