Move multiprocessing test-case file to the right place (#12727)

stdlib/@tests/test_cases/multiprocessing/check_pipe_connections.py

@@ -0,0 +1,31 @@
+from __future__ import annotations
+
+import sys
+from multiprocessing.connection import Pipe
+
+if sys.platform != "win32":
+    from multiprocessing.connection import Connection
+else:
+    from multiprocessing.connection import PipeConnection as Connection
+
+
+# Unfortunately, we cannot validate that both connections have the same, but inverted generic types,
+# since TypeVars scoped entirely within a return annotation is unspecified in the spec.
+# Pipe[str, int]() -> tuple[Connection[str, int], Connection[int, str]]
+
+a: Connection[str, int]
+b: Connection[int, str]
+a, b = Pipe()
+
+connections: tuple[Connection[str, int], Connection[int, str]] = Pipe()
+a, b = connections
+
+a.send("test")
+a.send(0)  # type: ignore
+test1: str = b.recv()
+test2: int = b.recv()  # type: ignore
+
+b.send("test")  # type: ignore
+b.send(0)
+test3: str = a.recv()  # type: ignore
+test4: int = a.recv()