Turn PytestDeprecationWarning into error

Fix #5402

changelog/5402.removal.rst

@@ -0,0 +1,23 @@
+**PytestDeprecationWarning are now errors by default.**
+
+Following our plan to remove deprecated features with as little disruption as
+possible, all warnings of type ``PytestDeprecationWarning`` now generate errors
+instead of warning messages.
+
+**The affected features will be effectively removed in pytest 5.1**, so please consult the
+`Deprecations and Removals <https://docs.pytest.org/en/latest/deprecations.html>`__
+section in the docs for directions on how to update existing code.
+
+In the pytest ``5.0.X`` series, it is possible to change the errors back into warnings as a stop
+gap measure by adding this to your ``pytest.ini`` file:
+
+.. code-block:: ini
+
+    [pytest]
+    filterwarnings =
+        ignore::pytest.PytestDeprecationWarning
+
+But this will stop working when pytest ``5.1`` is released.
+
+**If you have concerns** about the removal of a specific feature, please add a
+comment to `#5402 <https://github.com/pytest-dev/pytest/issues/5402>`__.

src/_pytest/warnings.py

@@ -75,6 +75,7 @@ def catch_warnings_for_item(config, ihook, when, item):
             warnings.filterwarnings("always", category=PendingDeprecationWarning)
 
         warnings.filterwarnings("error", category=pytest.RemovedInPytest4Warning)
+        warnings.filterwarnings("error", category=pytest.PytestDeprecationWarning)
 
         # filters should have this precedence: mark, cmdline options, ini
         # filters should be applied in the inverse order of precedence

testing/python/fixtures.py

@@ -1138,7 +1138,6 @@ class TestFixtureUsages:
         values = reprec.getfailedcollections()
         assert len(values) == 1
 
-    @pytest.mark.filterwarnings("ignore::pytest.PytestDeprecationWarning")
     def test_request_can_be_overridden(self, testdir):
         testdir.makepyfile(
             """
@@ -1151,7 +1150,7 @@ class TestFixtureUsages:
                 assert request.a == 1
         """
         )
-        reprec = testdir.inline_run()
+        reprec = testdir.inline_run("-Wignore::pytest.PytestDeprecationWarning")
         reprec.assertoutcome(passed=1)
 
     def test_usefixtures_marker(self, testdir):

testing/test_warnings.py

@@ -528,6 +528,37 @@ def test_removed_in_pytest4_warning_as_error(testdir, change_default):
         result.stdout.fnmatch_lines(["* 1 passed in *"])
 
 
+@pytest.mark.parametrize("change_default", [None, "ini", "cmdline"])
+def test_deprecation_warning_as_error(testdir, change_default):
+    testdir.makepyfile(
+        """
+        import warnings, pytest
+        def test():
+            warnings.warn(pytest.PytestDeprecationWarning("some warning"))
+    """
+    )
+    if change_default == "ini":
+        testdir.makeini(
+            """
+            [pytest]
+            filterwarnings =
+                ignore::pytest.PytestDeprecationWarning
+        """
+        )
+
+    args = (
+        ("-Wignore::pytest.PytestDeprecationWarning",)
+        if change_default == "cmdline"
+        else ()
+    )
+    result = testdir.runpytest(*args)
+    if change_default is None:
+        result.stdout.fnmatch_lines(["* 1 failed in *"])
+    else:
+        assert change_default in ("ini", "cmdline")
+        result.stdout.fnmatch_lines(["* 1 passed in *"])
+
+
 class TestAssertionWarnings:
     @staticmethod
     def assert_result_warns(result, msg):