Include new --capture-mode=tee-sys option

Fix #4597

AUTHORS

@@ -52,6 +52,7 @@ Carl Friedrich Bolz
 Carlos Jenkins
 Ceridwen
 Charles Cloud
+Charles Machalow
 Charnjit SiNGH (CCSJ)
 Chris Lamb
 Christian Boelsen

changelog/4597.feature.rst

@@ -0,0 +1 @@
+New :ref:`--capture=tee-sys <capture-method>` option to allow both live printing and capturing of test output.

doc/en/capture.rst

@@ -21,18 +21,25 @@ file descriptors.  This allows to capture output from simple
 print statements as well as output from a subprocess started by
 a test.
 
+.. _capture-method:
+
 Setting capturing methods or disabling capturing
 -------------------------------------------------
 
-There are two ways in which ``pytest`` can perform capturing:
+There are three ways in which ``pytest`` can perform capturing:
 
-* file descriptor (FD) level capturing (default): All writes going to the
+* ``fd`` (file descriptor) level capturing (default): All writes going to the
   operating system file descriptors 1 and 2 will be captured.
 
 * ``sys`` level capturing: Only writes to Python files ``sys.stdout``
   and ``sys.stderr`` will be captured.  No capturing of writes to
   filedescriptors is performed.
 
+* ``tee-sys`` capturing: Python writes to ``sys.stdout`` and ``sys.stderr``
+  will be captured, however the writes will also be passed-through to
+  the actual ``sys.stdout`` and ``sys.stderr``. This allows output to be
+  'live printed' and captured for plugin use, such as junitxml (new in pytest 5.4).
+
 .. _`disable capturing`:
 
 You can influence output capturing mechanisms from the command line:
@@ -42,6 +49,8 @@ You can influence output capturing mechanisms from the command line:
     pytest -s                  # disable all capturing
     pytest --capture=sys       # replace sys.stdout/stderr with in-mem files
     pytest --capture=fd        # also point filedescriptors 1 and 2 to temp file
+    pytest --capture=tee-sys   # combines 'sys' and '-s', capturing sys.stdout/stderr
+                               # and passing it along to the actual sys.stdout/stderr
 
 .. _printdebugging:
 

src/_pytest/capture.py

@@ -11,6 +11,7 @@ from io import UnsupportedOperation
 from tempfile import TemporaryFile
 
 import pytest
+from _pytest.compat import CaptureAndPassthroughIO
 from _pytest.compat import CaptureIO
 from _pytest.fixtures import FixtureRequest
 
@@ -24,8 +25,8 @@ def pytest_addoption(parser):
         action="store",
         default="fd" if hasattr(os, "dup") else "sys",
         metavar="method",
-        choices=["fd", "sys", "no"],
-        help="per-test capturing method: one of fd|sys|no.",
+        choices=["fd", "sys", "no", "tee-sys"],
+        help="per-test capturing method: one of fd|sys|no|tee-sys.",
     )
     group._addoption(
         "-s",
@@ -90,6 +91,8 @@ class CaptureManager:
             return MultiCapture(out=True, err=True, Capture=SysCapture)
         elif method == "no":
             return MultiCapture(out=False, err=False, in_=False)
+        elif method == "tee-sys":
+            return MultiCapture(out=True, err=True, in_=False, Capture=TeeSysCapture)
         raise ValueError("unknown capturing method: %r" % method)  # pragma: no cover
 
     def is_capturing(self):
@@ -681,6 +684,19 @@ class SysCapture:
         self._old.flush()
 
 
+class TeeSysCapture(SysCapture):
+    def __init__(self, fd, tmpfile=None):
+        name = patchsysdict[fd]
+        self._old = getattr(sys, name)
+        self.name = name
+        if tmpfile is None:
+            if name == "stdin":
+                tmpfile = DontReadFromInput()
+            else:
+                tmpfile = CaptureAndPassthroughIO(self._old)
+        self.tmpfile = tmpfile
+
+
 class SysCaptureBinary(SysCapture):
     # Ignore type because it doesn't match the type in the superclass (str).
     EMPTY_BUFFER = b""  # type: ignore

src/_pytest/compat.py

@@ -13,6 +13,7 @@ from inspect import signature
 from typing import Any
 from typing import Callable
 from typing import Generic
+from typing import IO
 from typing import Optional
 from typing import overload
 from typing import Tuple
@@ -371,6 +372,16 @@ class CaptureIO(io.TextIOWrapper):
         return self.buffer.getvalue().decode("UTF-8")
 
 
+class CaptureAndPassthroughIO(CaptureIO):
+    def __init__(self, other: IO) -> None:
+        self._other = other
+        super().__init__()
+
+    def write(self, s) -> int:
+        super().write(s)
+        return self._other.write(s)
+
+
 if sys.version_info < (3, 5, 2):  # pragma: no cover
 
     def overload(f):  # noqa: F811

testing/acceptance_test.py

@@ -1285,3 +1285,28 @@ def test_pdb_can_be_rewritten(testdir):
         ]
     )
     assert result.ret == 1
+
+
+def test_tee_stdio_captures_and_live_prints(testdir):
+    testpath = testdir.makepyfile(
+        """
+        import sys
+        def test_simple():
+            print ("@this is stdout@")
+            print ("@this is stderr@", file=sys.stderr)
+    """
+    )
+    result = testdir.runpytest_subprocess(
+        testpath, "--capture=tee-sys", "--junitxml=output.xml"
+    )
+
+    # ensure stdout/stderr were 'live printed'
+    result.stdout.fnmatch_lines(["*@this is stdout@*"])
+    result.stderr.fnmatch_lines(["*@this is stderr@*"])
+
+    # now ensure the output is in the junitxml
+    with open(os.path.join(testdir.tmpdir.strpath, "output.xml"), "r") as f:
+        fullXml = f.read()
+
+    assert "<system-out>@this is stdout@\n</system-out>" in fullXml
+    assert "<system-err>@this is stderr@\n</system-err>" in fullXml

testing/test_capture.py

@@ -32,6 +32,10 @@ def StdCapture(out=True, err=True, in_=True):
     return capture.MultiCapture(out, err, in_, Capture=capture.SysCapture)
 
 
+def TeeStdCapture(out=True, err=True, in_=True):
+    return capture.MultiCapture(out, err, in_, Capture=capture.TeeSysCapture)
+
+
 class TestCaptureManager:
     def test_getmethod_default_no_fd(self, monkeypatch):
         from _pytest.capture import pytest_addoption
@@ -816,6 +820,25 @@ class TestCaptureIO:
         assert f.getvalue() == "foo\r\n"
 
 
+class TestCaptureAndPassthroughIO(TestCaptureIO):
+    def test_text(self):
+        sio = io.StringIO()
+        f = capture.CaptureAndPassthroughIO(sio)
+        f.write("hello")
+        s1 = f.getvalue()
+        assert s1 == "hello"
+        s2 = sio.getvalue()
+        assert s2 == s1
+        f.close()
+        sio.close()
+
+    def test_unicode_and_str_mixture(self):
+        sio = io.StringIO()
+        f = capture.CaptureAndPassthroughIO(sio)
+        f.write("\u00f6")
+        pytest.raises(TypeError, f.write, b"hello")
+
+
 def test_dontreadfrominput():
     from _pytest.capture import DontReadFromInput
 
@@ -1112,6 +1135,23 @@ class TestStdCapture:
             pytest.raises(IOError, sys.stdin.read)
 
 
+class TestTeeStdCapture(TestStdCapture):
+    captureclass = staticmethod(TeeStdCapture)
+
+    def test_capturing_error_recursive(self):
+        """ for TeeStdCapture since we passthrough stderr/stdout, cap1
+        should get all output, while cap2 should only get "cap2\n" """
+
+        with self.getcapture() as cap1:
+            print("cap1")
+            with self.getcapture() as cap2:
+                print("cap2")
+                out2, err2 = cap2.readouterr()
+                out1, err1 = cap1.readouterr()
+        assert out1 == "cap1\ncap2\n"
+        assert out2 == "cap2\n"
+
+
 class TestStdCaptureFD(TestStdCapture):
     pytestmark = needsosdup
     captureclass = staticmethod(StdCaptureFD)
@@ -1252,7 +1292,7 @@ def test_close_and_capture_again(testdir):
     )
 
 
-@pytest.mark.parametrize("method", ["SysCapture", "FDCapture"])
+@pytest.mark.parametrize("method", ["SysCapture", "FDCapture", "TeeSysCapture"])
 def test_capturing_and_logging_fundamentals(testdir, method):
     if method == "StdCaptureFD" and not hasattr(os, "dup"):
         pytest.skip("need os.dup")