Do not fail tests on our own deprecation warnings

Author: sbidoul

tests/lib/__init__.py

@@ -39,7 +39,6 @@
 from pip._internal.models.selection_prefs import SelectionPreferences
 from pip._internal.models.target_python import TargetPython
 from pip._internal.network.session import PipSession
-from pip._internal.utils.deprecation import DEPRECATION_MSG_PREFIX
 from tests.lib.venv import VirtualEnvironment
 from tests.lib.wheel import make_wheel
 
@@ -474,7 +473,7 @@ def _check_stderr(
         if allow_stderr_warning:
             continue
 
-        if line.startswith("WARNING: ") or line.startswith(DEPRECATION_MSG_PREFIX):
+        if line.startswith("WARNING: "):
             reason = (
                 "stderr has an unexpected warning "
                 "(pass allow_stderr_warning=True to permit this)"

tests/lib/test_lib.py

@@ -150,7 +150,6 @@ def test_run__allow_stderr_warning(self, script: PipTestEnvironment) -> None:
     @pytest.mark.parametrize(
         "prefix",
         (
-            "DEPRECATION",
             "WARNING",
             "ERROR",
         ),
@@ -167,7 +166,6 @@ def test_run__allow_stderr_error(
     @pytest.mark.parametrize(
         "prefix, expected_start",
         (
-            ("DEPRECATION", "stderr has an unexpected warning"),
             ("WARNING", "stderr has an unexpected warning"),
             ("ERROR", "stderr has an unexpected error"),
         ),