fix(capture): guard snap() against closed tmpfile (#14528)

src/_pytest/capture.py

@@ -449,6 +449,8 @@ class SysCapture(SysCaptureBase[str]):
 
     def snap(self) -> str:
         self._assert_state("snap", ("started", "suspended"))
+        if getattr(self.tmpfile, "closed", False):
+            return self.EMPTY_BUFFER
         assert isinstance(self.tmpfile, CaptureIO)
         res = self.tmpfile.getvalue()
         self.tmpfile.seek(0)
@@ -566,6 +568,8 @@ class FDCaptureBinary(FDCaptureBase[bytes]):
 
     def snap(self) -> bytes:
         self._assert_state("snap", ("started", "suspended"))
+        if getattr(self.tmpfile, "closed", False):
+            return self.EMPTY_BUFFER
         self.tmpfile.seek(0)
         res = self.tmpfile.buffer.read()
         self.tmpfile.seek(0)
@@ -588,6 +592,8 @@ class FDCapture(FDCaptureBase[str]):
 
     def snap(self) -> str:
         self._assert_state("snap", ("started", "suspended"))
+        if getattr(self.tmpfile, "closed", False):
+            return self.EMPTY_BUFFER
         self.tmpfile.seek(0)
         res = self.tmpfile.read()
         self.tmpfile.seek(0)

testing/test_capture.py

@@ -1750,3 +1750,30 @@ def pytest_terminal_summary(config):
     match = re.search(r"^value: '(.*)'\r?$", rest, re.MULTILINE)
     assert match is not None
     assert match.group(1) == "hi"
+
+
+def test_snap_on_closed_tmpfile() -> None:
+    """Regression test for #14528: snap() should not crash when tmpfile is closed."""
+    # FDCapture
+    cap = capture.FDCapture(1)
+    cap.start()
+    cap.done()
+    assert cap.snap() == ""
+
+    # FDCaptureBinary
+    capb = capture.FDCaptureBinary(1)
+    capb.start()
+    capb.done()
+    assert capb.snap() == b""
+
+    # SysCapture
+    caps = capture.SysCapture(1)
+    caps.start()
+    caps.done()
+    assert caps.snap() == ""
+
+    # SysCaptureBinary
+    capsb = capture.SysCaptureBinary(1)
+    capsb.start()
+    capsb.done()
+    assert capsb.snap() == b""