finish migrating test_warning.py from testdir to pytester

Author: bot2x

testing/test_warnings.py

@@ -6,7 +6,6 @@
 
 import pytest
 from _pytest.fixtures import FixtureRequest
-from _pytest.pytester import Testdir
 from _pytest.pytester import Pytester
 
 WARNINGS_SUMMARY_HEADER = "warnings summary"
@@ -18,7 +17,7 @@ def pyfile_with_warnings(pytester: Pytester, request: FixtureRequest) -> str:
     pytester.syspathinsert()
     test_name = request.function.__name__
     module_name = test_name.lstrip("test_") + "_module"
-    test_file = testdir.makepyfile(
+    test_file = pytester.makepyfile(
         """
         import {module_name}
         def test_func():
@@ -665,7 +664,7 @@ class CapturedWarnings:
             def pytest_warning_recorded(cls, warning_message, when, nodeid, location):
                 cls.captured.append((warning_message, location))
 
-        testdir.plugins = [CapturedWarnings()]
+        pytester.plugins = [CapturedWarnings()]
 
         return CapturedWarnings