Show deprecation warnings by default if no other filters are configured

Fix pytest-dev#2908

Author: nicoddemus

changelog/2908.feature.rst

@@ -0,0 +1,3 @@
+``DeprecationWarning`` and ``PendingDeprecationWarning`` are now shown by default if no other warning filter is
+configured. This makes pytest compliant with
+`PEP-0506 <https://www.python.org/dev/peps/pep-0565/#recommended-filter-settings-for-test-runners>`_.

doc/en/warnings.rst

@@ -36,8 +36,6 @@ Running pytest now produces this output::
     -- Docs: http://doc.pytest.org/en/latest/warnings.html
     =================== 1 passed, 1 warnings in 0.12 seconds ===================
 
-Pytest by default catches all warnings except for ``DeprecationWarning`` and ``PendingDeprecationWarning``.
-
 The ``-W`` flag can be passed to control which warnings will be displayed or even turn
 them into errors::
 
@@ -78,6 +76,32 @@ Both ``-W`` command-line option and ``filterwarnings`` ini option are based on P
 `-W option`_ and `warnings.simplefilter`_, so please refer to those sections in the Python
 documentation for other examples and advanced usage.
 
+Disabling warning summary
+-------------------------
+
+Although not recommended, you can use the ``--disable-warnings`` command-line option to suppress the
+warning summary entirely from the test run output.
+
+
+DeprecationWarning and PendingDeprecationWarning
+------------------------------------------------
+
+.. versionadded:: 3.8
+
+By default pytest will display ``DeprecationWarning`` and ``PendingDeprecationWarning`` if no other warning filters
+are configured. This complies with `PEP-0506 <https://www.python.org/dev/peps/pep-0565/#recommended-filter-settings-for-test-runners>`_ which suggests that those warnings should
+be shown by default by test runners.
+
+To disable this behavior, you might define any warnings filter either in the command-line or in the ini file, but
+if you don't have any other warnings to filter you can use:
+
+.. code-block:: ini
+
+    [pytest]
+    filterwarnings =
+        ignore::DeprecationWarning
+        ignore::PendingDeprecationWarning
+
 
 .. _`filterwarnings`:
 

src/_pytest/warnings.py

@@ -1,5 +1,6 @@
 from __future__ import absolute_import, division, print_function
 
+import sys
 import warnings
 from contextlib import contextmanager
 
@@ -69,6 +70,8 @@ def catch_warnings_for_item(config, ihook, item):
     args = config.getoption("pythonwarnings") or []
     inifilters = config.getini("filterwarnings")
     with warnings.catch_warnings(record=True) as log:
+        filters_configured = args or inifilters or sys.warnoptions
+
         for arg in args:
             warnings._setoption(arg)
 
@@ -79,6 +82,11 @@ def catch_warnings_for_item(config, ihook, item):
             for mark in item.iter_markers(name="filterwarnings"):
                 for arg in mark.args:
                     warnings._setoption(arg)
+                    filters_configured = True
+
+        if not filters_configured:
+            warnings.filterwarnings("always", category=DeprecationWarning)
+            warnings.filterwarnings("always", category=PendingDeprecationWarning)
 
         yield
 

testing/python/collect.py

@@ -8,10 +8,6 @@
 from _pytest.main import EXIT_NOTESTSCOLLECTED
 from _pytest.nodes import Collector
 
-ignore_parametrized_marks = pytest.mark.filterwarnings(
-    "ignore:Applying marks directly to parameters"
-)
-
 
 class TestModule(object):
     def test_failing_import(self, testdir):
@@ -456,6 +452,13 @@ def test_setuplist():
 
 
 class TestFunction(object):
+    @pytest.fixture
+    def ignore_parametrized_marks_args(self):
+        """Provides arguments to pytester.runpytest() to ignore the warning about marks being applied directly
+        to parameters.
+        """
+        return ("-W", "ignore:Applying marks directly to parameters")
+
     def test_getmodulecollector(self, testdir):
         item = testdir.getitem("def test_func(): pass")
         modcol = item.getparent(pytest.Module)
@@ -669,7 +672,7 @@ def test_it(fix1):
         rec = testdir.inline_run()
         rec.assertoutcome(passed=1)
 
-    @ignore_parametrized_marks
+    @pytest.mark.filterwarnings("ignore:Applying marks directly to parameters")
     def test_parametrize_with_mark(self, testdir):
         items = testdir.getitems(
             """
@@ -755,8 +758,7 @@ def test2(self, x, y):
         assert colitems[2].name == "test2[a-c]"
         assert colitems[3].name == "test2[b-c]"
 
-    @ignore_parametrized_marks
-    def test_parametrize_skipif(self, testdir):
+    def test_parametrize_skipif(self, testdir, ignore_parametrized_marks_args):
         testdir.makepyfile(
             """
             import pytest
@@ -768,11 +770,10 @@ def test_skip_if(x):
                 assert x < 2
         """
         )
-        result = testdir.runpytest()
+        result = testdir.runpytest(*ignore_parametrized_marks_args)
         result.stdout.fnmatch_lines("* 2 passed, 1 skipped in *")
 
-    @ignore_parametrized_marks
-    def test_parametrize_skip(self, testdir):
+    def test_parametrize_skip(self, testdir, ignore_parametrized_marks_args):
         testdir.makepyfile(
             """
             import pytest
@@ -784,11 +785,10 @@ def test_skip(x):
                 assert x < 2
         """
         )
-        result = testdir.runpytest()
+        result = testdir.runpytest(*ignore_parametrized_marks_args)
         result.stdout.fnmatch_lines("* 2 passed, 1 skipped in *")
 
-    @ignore_parametrized_marks
-    def test_parametrize_skipif_no_skip(self, testdir):
+    def test_parametrize_skipif_no_skip(self, testdir, ignore_parametrized_marks_args):
         testdir.makepyfile(
             """
             import pytest
@@ -800,11 +800,10 @@ def test_skipif_no_skip(x):
                 assert x < 2
         """
         )
-        result = testdir.runpytest()
+        result = testdir.runpytest(*ignore_parametrized_marks_args)
         result.stdout.fnmatch_lines("* 1 failed, 2 passed in *")
 
-    @ignore_parametrized_marks
-    def test_parametrize_xfail(self, testdir):
+    def test_parametrize_xfail(self, testdir, ignore_parametrized_marks_args):
         testdir.makepyfile(
             """
             import pytest
@@ -816,11 +815,10 @@ def test_xfail(x):
                 assert x < 2
         """
         )
-        result = testdir.runpytest()
+        result = testdir.runpytest(*ignore_parametrized_marks_args)
         result.stdout.fnmatch_lines("* 2 passed, 1 xfailed in *")
 
-    @ignore_parametrized_marks
-    def test_parametrize_passed(self, testdir):
+    def test_parametrize_passed(self, testdir, ignore_parametrized_marks_args):
         testdir.makepyfile(
             """
             import pytest
@@ -832,11 +830,10 @@ def test_xfail(x):
                 pass
         """
         )
-        result = testdir.runpytest()
+        result = testdir.runpytest(*ignore_parametrized_marks_args)
         result.stdout.fnmatch_lines("* 2 passed, 1 xpassed in *")
 
-    @ignore_parametrized_marks
-    def test_parametrize_xfail_passed(self, testdir):
+    def test_parametrize_xfail_passed(self, testdir, ignore_parametrized_marks_args):
         testdir.makepyfile(
             """
             import pytest
@@ -848,7 +845,7 @@ def test_passed(x):
                 pass
         """
         )
-        result = testdir.runpytest()
+        result = testdir.runpytest(*ignore_parametrized_marks_args)
         result.stdout.fnmatch_lines("* 3 passed in *")
 
     def test_function_original_name(self, testdir):

testing/test_warnings.py

@@ -326,6 +326,7 @@ def pytest_warning_captured(self, warning_message, when, item):
 @pytest.mark.filterwarnings("always")
 def test_collection_warnings(testdir):
     """
+    Check that we also capture warnings issued during test collection (#3251).
     """
     testdir.makepyfile(
         """
@@ -346,3 +347,75 @@ def test_foo():
             "* 1 passed, 1 warnings*",
         ]
     )
+
+
+class TestDeprecationWarningsByDefault:
+    """
+    Note: all pytest runs are executed in a subprocess so we don't inherit warning filters
+    from pytest's own test suite
+    """
+
+    def create_file(self, testdir, mark=""):
+        testdir.makepyfile(
+            """
+            import pytest, warnings
+
+            warnings.warn(DeprecationWarning("collection"))
+
+            {mark}
+            def test_foo():
+                warnings.warn(PendingDeprecationWarning("test run"))
+        """.format(
+                mark=mark
+            )
+        )
+
+    def test_shown_by_default(self, testdir):
+        self.create_file(testdir)
+        result = testdir.runpytest_subprocess()
+        result.stdout.fnmatch_lines(
+            [
+                "*== %s ==*" % WARNINGS_SUMMARY_HEADER,
+                "*test_shown_by_default.py:3: DeprecationWarning: collection",
+                "*test_shown_by_default.py:7: PendingDeprecationWarning: test run",
+                "* 1 passed, 2 warnings*",
+            ]
+        )
+
+    def test_hidden_by_ini(self, testdir):
+        self.create_file(testdir)
+        testdir.makeini(
+            """
+            [pytest]
+            filterwarnings = once::UserWarning
+        """
+        )
+        result = testdir.runpytest_subprocess()
+        assert WARNINGS_SUMMARY_HEADER not in result.stdout.str()
+
+    def test_hidden_by_mark(self, testdir):
+        """Should hide the deprecation warning from the function, but the warning during collection should
+        be displayed normally.
+        """
+        self.create_file(
+            testdir, mark='@pytest.mark.filterwarnings("once::UserWarning")'
+        )
+        result = testdir.runpytest_subprocess()
+        result.stdout.fnmatch_lines(
+            [
+                "*== %s ==*" % WARNINGS_SUMMARY_HEADER,
+                "*test_hidden_by_mark.py:3: DeprecationWarning: collection",
+                "* 1 passed, 1 warnings*",
+            ]
+        )
+
+    def test_hidden_by_cmdline(self, testdir):
+        self.create_file(testdir)
+        result = testdir.runpytest_subprocess("-W", "once::UserWarning")
+        assert WARNINGS_SUMMARY_HEADER not in result.stdout.str()
+
+    def test_hidden_by_system(self, testdir, monkeypatch):
+        self.create_file(testdir)
+        monkeypatch.setenv(str("PYTHONWARNINGS"), str("once::UserWarning"))
+        result = testdir.runpytest_subprocess()
+        assert WARNINGS_SUMMARY_HEADER not in result.stdout.str()