try adding a test

Author: oconnor663

.github/workflows/ci.yml

@@ -12,7 +12,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.9", "3.10", "3.11", "3.12", "3.13", "3.14"]
+        python-version: ["3.9", "3.10", "3.11", "3.12", "3.13", "3.13t", "3.14", "3.14t"]
         os: [ubuntu-latest, windows-latest, macOS-latest]
 
     steps:

test_duct.py

@@ -70,9 +70,7 @@ def head_bytes(c):
         stdout = os.fdopen(1, 'w')
         input_str = stdin.read({0})
         stdout.write(input_str)
-        """.format(
-            c
-        )
+        """.format(c)
     )
     return cmd("python", "-c", code)
 
@@ -86,9 +84,7 @@ def echo_var(var_name):
         """\
         import os
         print(os.environ.get("{0}", ""))
-        """.format(
-            var_name
-        )
+        """.format(var_name)
     )
     return cmd("python", "-c", code)
 
@@ -103,9 +99,7 @@ def replace(a, b):
         import sys
         input_str = sys.stdin.read()
         sys.stdout.write(input_str.replace({0}, {1}))
-        """.format(
-            repr(a), repr(b)
-        )
+        """.format(repr(a), repr(b))
     )
     return cmd("python", "-c", code)
 
@@ -684,9 +678,7 @@ def test_kill_with_grandchild():
 print("started")
 sys.stdout.flush()
 p.wait()
-""".format(
-        grandchild_code
-    )
+""".format(grandchild_code)
 
     # Capturing stderr means an IO thread is spawned, even though we're using a
     # ReaderHandle to read stdout. What we're testing here is that kill()
@@ -1005,3 +997,39 @@ def test_zombies_reaped():
         while ps_observes_pid(pid):
             tries += 1
             assert tries < 100, f"child #{i} (PID {pid}) never went away?"
+
+
+def test_pipe_inheritance():
+    waiters = []
+    threads = []
+
+    def reader_fn():
+        # Open a pipe for the child to read from. This can deadlock if a waiter
+        # inherits this pipe and keeps it open.
+        reader, writer = os.pipe()
+        os.fdopen(writer, "wb").write(b"foo")
+        output = cat_cmd().stdin_file(reader).read()
+        assert output == "foo"
+
+    def waiter_fn():
+        # Spawn a child that won't exit until we kill it. This is intended to
+        # keep pipes open if they're inherited unintentionally. Without
+        # something like this, we'd need an inheritance *cycle* between
+        # readers, which might be unlikely.
+        waiters.append(sleep_cmd(365 * 24 * 60 * 60).unchecked().start())
+
+    for _ in range(100):
+        thread = threading.Thread(target=reader_fn)
+        thread.start()
+        threads.append(thread)
+
+        thread = threading.Thread(target=waiter_fn)
+        thread.start()
+        threads.append(thread)
+
+    for thread in threads:
+        thread.join()
+
+    for waiter in waiters:
+        waiter.kill()
+        waiter.wait()