Add test for finalizer, which broke in 3.8 due to underlying change i…

…n Pool._repopulate_pool, which also manifests as a hang in long-running tests that manage to kill all the worker processes.

green/test/test_integration.py

@@ -0,0 +1,60 @@
+import multiprocessing
+import os
+from pathlib import PurePath
+import subprocess
+import sys
+import tempfile
+from textwrap import dedent
+import unittest
+
+try:
+    from unittest.mock import MagicMock
+except:
+    from mock import MagicMock
+
+from green import cmdline
+
+
+class TestFinalizer(unittest.TestCase):
+    def setUp(self):
+        self.tmpdir = tempfile.mkdtemp()
+
+    def test_finalizer(self):
+        """
+        Test that the finalizer works on Python 3.8+
+        """
+        sub_tmpdir = tempfile.mkdtemp(dir=self.tmpdir)
+        for i in range(multiprocessing.cpu_count() * 2):
+            fh = open(os.path.join(sub_tmpdir, f"test_finalizer{i}.py"), "w")
+            fh.write(
+                dedent(
+                    f"""
+                import unittest
+                class Pass{i}(unittest.TestCase):
+                    def test_pass{i}(self):
+                        pass
+                def msg():
+                    print("finalizer worked")
+                """
+                )
+            )
+            fh.close()
+        args = [
+            sys.executable,
+            "-m",
+            "green.cmdline",
+            "--finalizer=test_finalizer0.msg",
+            "--maxtasksperchild=1",
+        ]
+        pythonpath = str(PurePath(__file__).parent.parent.parent)
+        print(pythonpath)
+        print(
+            subprocess.run(
+                args,
+                cwd=sub_tmpdir,
+                stdout=subprocess.PIPE,
+                stderr=subprocess.STDOUT,
+                env={"PYTHONPATH": pythonpath},
+                timeout=10,
+            ).stdout.decode("utf-8")
+        )