fix: avoid replaying tee capture output

CHANGELOG.md

@@ -7,6 +7,9 @@ releases are available on [PyPI](https://pypi.org/project/pytask) and
 
 ## Unreleased
 
+- [#970](https://github.com/pytask-dev/pytask/pull/970) prevents tee-sys capture from
+  replaying output that was already displayed when capture stops before its buffer is
+  read.
 - [#968](https://github.com/pytask-dev/pytask/pull/968) improves the performance of file
   descriptor capture for tasks that produce no output.
 - Documents the pytest provenance of the adapted debugging, marker, and warning

src/_pytask/capture.py

@@ -769,7 +769,11 @@ def start_capturing(self) -> None:
 
     def stop_capturing(self) -> None:
         if self._capturing is not None:
-            self._capturing.pop_outerr_to_orig()
+            if self._method == CaptureMethod.TEE_SYS:
+                # TeeCaptureIO already forwarded the output to the original streams.
+                self._capturing.readouterr()
+            else:
+                self._capturing.pop_outerr_to_orig()
             self._capturing.stop_capturing()
             self._capturing = None
 

tests/test_capture.py

@@ -187,6 +187,28 @@ def TeeStdCapture(  # noqa: N802
 
 
 class TestCaptureManager:
+    def test_stop_capturing_does_not_replay_tee_output(self, capsys):
+        capman = CaptureManager(CaptureMethod.TEE_SYS)
+        capman.start_capturing()
+        print("stdout")
+        print("stderr", file=sys.stderr)
+
+        capman.stop_capturing()
+
+        captured = capsys.readouterr()
+        assert captured == ("stdout\n", "stderr\n")
+
+    def test_stop_capturing_replays_non_tee_output(self, capsys):
+        capman = CaptureManager(CaptureMethod.SYS)
+        capman.start_capturing()
+        print("stdout")
+        print("stderr", file=sys.stderr)
+
+        capman.stop_capturing()
+
+        captured = capsys.readouterr()
+        assert captured == ("stdout\n", "stderr\n")
+
     @pytest.mark.parametrize(
         "method", [CaptureMethod.NO, CaptureMethod.SYS, CaptureMethod.FD]
     )