fix: correct error message for stdout pipe check in run_process (#3416)

* fix: correct error message for stdout pipe check in run_process

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---------

Co-authored-by: nightcityblade <nightcityblade@gmail.com>
Co-authored-by: A5rocks <git@helvetica.moe>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: 4 people

newsfragments/3409.bugfix.rst

@@ -0,0 +1 @@
+Fixed incorrect error message in ``run_process``: the ``stdout`` pipe check now correctly says "stdout" instead of "stdin".

src/trio/_subprocess.py

@@ -675,7 +675,7 @@ async def my_deliver_cancel(process):
     if task_status is trio.TASK_STATUS_IGNORED:
         if stdin is subprocess.PIPE:
             raise ValueError(
-                "stdout=subprocess.PIPE is only valid with nursery.start, "
+                "stdin=subprocess.PIPE is only valid with nursery.start, "
                 "since that's the only way to access the pipe; use nursery.start "
                 "or pass the data you want to write directly",
             )

src/trio/_tests/test_subprocess.py

@@ -367,9 +367,10 @@ async def test_run() -> None:
     with pytest.raises(UnicodeError):
         await run_process(CAT, stdin="oh no, it's text")
 
-    pipe_stdout_error = r"^stdout=subprocess\.PIPE is only valid with nursery\.start, since that's the only way to access the pipe(; use nursery\.start or pass the data you want to write directly)*$"
-    with pytest.raises(ValueError, match=pipe_stdout_error):
+    pipe_stdin_error = r"^stdin=subprocess\.PIPE is only valid with nursery\.start, since that's the only way to access the pipe; use nursery\.start or pass the data you want to write directly$"
+    with pytest.raises(ValueError, match=pipe_stdin_error):
         await run_process(CAT, stdin=subprocess.PIPE)
+    pipe_stdout_error = r"^stdout=subprocess\.PIPE is only valid with nursery\.start, since that's the only way to access the pipe$"
     with pytest.raises(ValueError, match=pipe_stdout_error):
         await run_process(CAT, stdout=subprocess.PIPE)
     with pytest.raises(