Add in --strict-config flag to force warnings to errors

src/_pytest/config/__init__.py

@@ -1020,7 +1020,7 @@ class Config:
             )
 
         self._checkversion()
-        self._validatekeys()
+        self._validatekeys(args)
         self._consider_importhook(args)
         self.pluginmanager.consider_preparse(args, exclude_only=False)
         if not os.environ.get("PYTEST_DISABLE_PLUGIN_AUTOLOAD"):
@@ -1073,9 +1073,12 @@ class Config:
                     )
                 )
 
-    def _validatekeys(self):
+    def _validatekeys(self, args: Sequence[str]):
         for key in self._get_unknown_ini_keys():
-            sys.stderr.write("WARNING: unknown config ini key: {}\n".format(key))
+            message = "Unknown config ini key: {}\n".format(key)
+            if "--strict-config" in args:
+                fail(message, pytrace=False)
+            sys.stderr.write("WARNING: {}".format(message))
 
     def _get_unknown_ini_keys(self) -> List[str]:
         parser_inicfg = self._parser._inidict

src/_pytest/main.py

@@ -70,6 +70,11 @@ def pytest_addoption(parser):
         default=0,
         help="exit after first num failures or errors.",
     )
+    group._addoption(
+        "--strict-config",
+        action="store_true",
+        help="invalid ini keys for the `pytest` section of the configuration file raise errors.",
+    )
     group._addoption(
         "--strict-markers",
         "--strict",

testing/test_config.py

@@ -148,7 +148,7 @@ class TestParseIni:
         assert result.ret == 0
 
     @pytest.mark.parametrize(
-        "ini_file_text, invalid_keys, stderr_output",
+        "ini_file_text, invalid_keys, stderr_output, exception_text",
         [
             (
                 """
@@ -158,9 +158,10 @@ class TestParseIni:
           """,
                 ["unknown_ini", "another_unknown_ini"],
                 [
-                    "WARNING: unknown config ini key: unknown_ini",
-                    "WARNING: unknown config ini key: another_unknown_ini",
+                    "WARNING: Unknown config ini key: unknown_ini",
+                    "WARNING: Unknown config ini key: another_unknown_ini",
                 ],
+                "Unknown config ini key: unknown_ini",
             ),
             (
                 """
@@ -169,7 +170,8 @@ class TestParseIni:
           minversion = 5.0.0
           """,
                 ["unknown_ini"],
-                ["WARNING: unknown config ini key: unknown_ini"],
+                ["WARNING: Unknown config ini key: unknown_ini"],
+                "Unknown config ini key: unknown_ini",
             ),
             (
                 """
@@ -180,6 +182,7 @@ class TestParseIni:
           """,
                 [],
                 [],
+                "",
             ),
             (
                 """
@@ -188,11 +191,12 @@ class TestParseIni:
           """,
                 [],
                 [],
+                "",
             ),
         ],
     )
-    def test_invalid_ini_keys_generate_warings(
-        self, testdir, ini_file_text, invalid_keys, stderr_output
+    def test_invalid_ini_keys(
+        self, testdir, ini_file_text, invalid_keys, stderr_output, exception_text
     ):
         testdir.tmpdir.join("pytest.ini").write(textwrap.dedent(ini_file_text))
         config = testdir.parseconfig()
@@ -203,6 +207,10 @@ class TestParseIni:
         result = testdir.runpytest()
         result.stderr.fnmatch_lines(stderr_output)
 
+        if stderr_output:
+            with pytest.raises(pytest.fail.Exception, match=exception_text):
+                testdir.runpytest("--strict-config")
+
 
 class TestConfigCmdlineParsing:
     def test_parsing_again_fails(self, testdir):