Add type tests

Author: A5rocks

src/trio/_tests/type_tests/subprocesses.py

@@ -0,0 +1,21 @@
+import sys
+
+import trio
+
+
+async def test() -> None:
+    # this could test more by using platform checks, but currently this
+    # is just regression tests + sanity checks.
+    await trio.run_process("python", executable="ls")
+    await trio.lowlevel.open_process("python", executable="ls")
+
+    await trio.run_process("python", capture_stdout=True)
+    await trio.lowlevel.open_process("python", capture_stdout=True)  # type: ignore[call-arg]
+
+    if sys.platform != "win32" and sys.version_info >= (3, 9):
+        await trio.run_process("python", extra_groups=[5])
+        await trio.lowlevel.open_process("python", extra_groups=[5])
+
+        # 3.11+:
+        await trio.run_process("python", process_group=5)  # type: ignore[call-arg]
+        await trio.lowlevel.open_process("python", process_group=5)  # type: ignore[call-arg]