Fix test suite when PYTEST_PLUGINS is set

Fixes #12647

Author: TobiMcNamobi

changelog/12647.contrib.rst

@@ -0,0 +1 @@
+Fixed running the test suite with the ``hypothesis`` pytest plugin.

testing/test_helpconfig.py

@@ -8,6 +8,7 @@
 
 def test_version_verbose(pytester: Pytester, pytestconfig, monkeypatch) -> None:
     monkeypatch.delenv("PYTEST_DISABLE_PLUGIN_AUTOLOAD")
+    monkeypatch.delenv("PYTEST_PLUGINS", raising=False)
     result = pytester.runpytest("--version", "--version")
     assert result.ret == 0
     result.stdout.fnmatch_lines([f"*pytest*{pytest.__version__}*imported from*"])
@@ -17,6 +18,7 @@ def test_version_verbose(pytester: Pytester, pytestconfig, monkeypatch) -> None:
 
 def test_version_less_verbose(pytester: Pytester, pytestconfig, monkeypatch) -> None:
     monkeypatch.delenv("PYTEST_DISABLE_PLUGIN_AUTOLOAD")
+    monkeypatch.delenv("PYTEST_PLUGINS", raising=False)
     result = pytester.runpytest("--version")
     assert result.ret == 0
     result.stdout.fnmatch_lines([f"pytest {pytest.__version__}"])

testing/test_terminal.py

@@ -859,6 +859,7 @@ def test_header_trailer_info(
         self, monkeypatch: MonkeyPatch, pytester: Pytester, request
     ) -> None:
         monkeypatch.delenv("PYTEST_DISABLE_PLUGIN_AUTOLOAD")
+        monkeypatch.delenv("PYTEST_PLUGINS", raising=False)
         pytester.makepyfile(
             """
             def test_passes():