Add capteesys capture fixture to bubble up output to --capture handler

doc/en/how-to/capture-stdout-stderr.rst

@@ -4,6 +4,11 @@
 How to capture stdout/stderr output
 =========================================================
 
+Pytest can intercept stdout and stderr by using the ``--capture=`` command-line
+or argument or by using fixtures. The flag ``--capture=`` configures reporting,
+whereas the fixtures offer somewhat more granular control and allow inspection
+during testing. The reports can customized with the `-r flag <../reference/reference.html#command-line-flags>`_.
+
 Default stdout/stderr/stdin capturing behaviour
 ---------------------------------------------------------
 
@@ -106,8 +111,8 @@ of the failing function and hide the other one:
 Accessing captured output from a test function
 ---------------------------------------------------
 
-The :fixture:`capsys`, :fixture:`capsysbinary`, :fixture:`capfd`, and :fixture:`capfdbinary` fixtures
-allow access to ``stdout``/``stderr`` output created during test execution.
+The :fixture:`capsys`, :fixture:`capteesys`, :fixture:`capsysbinary`, :fixture:`capfd`, and :fixture:`capfdbinary`
+fixtures allow access to ``stdout``/``stderr`` output created during test execution.
 
 Here is an example test function that performs some output related checks:
 

doc/en/reference/fixtures.rst

@@ -32,6 +32,10 @@ Built-in fixtures
    :fixture:`capsys`
         Capture, as text, output to ``sys.stdout`` and ``sys.stderr``.
 
+   :fixture:`capteesys`
+        Capture in the same manner as :fixture:`capsys`, but also pass text
+        through according to ``--capture=``.
+
    :fixture:`capsysbinary`
         Capture, as bytes, output to ``sys.stdout`` and ``sys.stderr``.
 

doc/en/reference/reference.rst

@@ -402,6 +402,16 @@ capsys
 .. autoclass:: pytest.CaptureFixture()
     :members:
 
+.. fixture:: capteesys
+
+capteesys
+~~~~~~~~~
+
+**Tutorial**: :ref:`captures`
+
+.. autofunction:: _pytest.capture.capteesys()
+    :no-auto-options:
+
 .. fixture:: capsysbinary
 
 capsysbinary

src/_pytest/capture.py

@@ -902,11 +902,13 @@ def __init__(
         captureclass: type[CaptureBase[AnyStr]],
         request: SubRequest,
         *,
+        config: dict[str, Any] | None = None,
         _ispytest: bool = False,
     ) -> None:
         check_ispytest(_ispytest)
         self.captureclass: type[CaptureBase[AnyStr]] = captureclass
         self.request = request
+        self._config = config if config else {}
         self._capture: MultiCapture[AnyStr] | None = None
         self._captured_out: AnyStr = self.captureclass.EMPTY_BUFFER
         self._captured_err: AnyStr = self.captureclass.EMPTY_BUFFER
@@ -915,8 +917,8 @@ def _start(self) -> None:
         if self._capture is None:
             self._capture = MultiCapture(
                 in_=None,
-                out=self.captureclass(1),
-                err=self.captureclass(2),
+                out=self.captureclass(1, **self._config),
+                err=self.captureclass(2, **self._config),
             )
             self._capture.start_capturing()
 
@@ -1002,6 +1004,41 @@ def test_output(capsys):
     capman.unset_fixture()
 
 
+@fixture
+def capteesys(request: SubRequest) -> Generator[CaptureFixture[str]]:
+    r"""Enable simultaneous text capturing and pass-through of writes
+    to ``sys.stdout`` and ``sys.stderr`` as defined by ``--capture=``.
+
+
+    The captured output is made available via ``capteesys.readouterr()`` method
+    calls, which return a ``(out, err)`` namedtuple.
+    ``out`` and ``err`` will be ``text`` objects.
+
+    The output is also passed-through, allowing it to be "live-printed",
+    reported, or both as defined by ``--capture=``.
+
+    Returns an instance of :class:`CaptureFixture[str] <pytest.CaptureFixture>`.
+
+    Example:
+
+    .. code-block:: python
+
+        def test_output(capsys):
+            print("hello")
+            captured = capteesys.readouterr()
+            assert captured.out == "hello\n"
+    """
+    capman: CaptureManager = request.config.pluginmanager.getplugin("capturemanager")
+    capture_fixture = CaptureFixture(
+        SysCapture, request, config=dict(tee=True), _ispytest=True
+    )
+    capman.set_fixture(capture_fixture)
+    capture_fixture._start()
+    yield capture_fixture
+    capture_fixture.close()
+    capman.unset_fixture()
+
+
 @fixture
 def capsysbinary(request: SubRequest) -> Generator[CaptureFixture[bytes]]:
     r"""Enable bytes capturing of writes to ``sys.stdout`` and ``sys.stderr``.

testing/test_capture.py

@@ -445,6 +445,25 @@ def test_hello(capsys):
         )
         reprec.assertoutcome(passed=1)
 
+    def test_capteesys(self, pytester: Pytester) -> None:
+        p = pytester.makepyfile(
+            """\
+            import sys
+            def test_one(capteesys):
+                print("sTdoUt")
+                print("sTdeRr", file=sys.stderr)
+                out, err = capteesys.readouterr()
+                assert out == "sTdoUt\\n"
+                assert err == "sTdeRr\\n"
+            """
+        )
+        # -rN and --capture=tee-sys means we'll read them on stdout/stderr,
+        # as opposed to both being reported on stdout
+        result = pytester.runpytest(p, "--quiet", "--quiet", "-rN", "--capture=tee-sys")
+        assert result.ret == ExitCode.OK
+        result.stdout.fnmatch_lines(["sTdoUt"])
+        result.stderr.fnmatch_lines(["sTdeRr"])
+
     def test_capsyscapfd(self, pytester: Pytester) -> None:
         p = pytester.makepyfile(
             """\