tests: isolate python env vars

tests/conftest.py

@@ -34,6 +34,7 @@ from poetry.utils.helpers import remove_directory
 from tests.helpers import TestLocker
 from tests.helpers import TestRepository
 from tests.helpers import get_package
+from tests.helpers import isolated_environment
 from tests.helpers import mock_clone
 from tests.helpers import mock_download
 
@@ -246,27 +247,19 @@ def pep517_metadata_mock(mocker: MockerFixture) -> None:
 
 @pytest.fixture
 def environ() -> Iterator[None]:
-    original_environ = dict(os.environ)
-
-    yield
-
-    os.environ.clear()
-    os.environ.update(original_environ)
+    with isolated_environment():
+        yield
 
 
 @pytest.fixture(autouse=True)
 def isolate_environ() -> Iterator[None]:
     """Ensure the environment is isolated from user configuration."""
-    original_environ = dict(os.environ)
-
-    for var in os.environ:
-        if var.startswith("POETRY_"):
-            del os.environ[var]
-
-    yield
+    with isolated_environment():
+        for var in os.environ:
+            if var.startswith("POETRY_") or var in {"PYTHONPATH", "VIRTUAL_ENV"}:
+                del os.environ[var]
 
-    os.environ.clear()
-    os.environ.update(original_environ)
+        yield
 
 
 @pytest.fixture(autouse=True)

tests/helpers.py

 from __future__ import annotations
 
+import contextlib
 import os
 import re
 import shutil
@@ -9,6 +10,7 @@ import urllib.parse
 from pathlib import Path
 from typing import TYPE_CHECKING
 from typing import Any
+from typing import Iterator
 
 from poetry.core.masonry.utils.helpers import escape_name
 from poetry.core.masonry.utils.helpers import escape_version
@@ -230,3 +232,21 @@ class TestRepository(Repository):
                 f"-{escape_version(package.version.text)}-py2.py3-none-any.whl"
             )
         ]
+
+
+@contextlib.contextmanager
+def isolated_environment(
+    environ: dict[str, Any] | None = None, clear: bool = False
+) -> Iterator[None]:
+    original_environ = dict(os.environ)
+
+    if clear:
+        os.environ.clear()
+
+    if environ:
+        os.environ.update(environ)
+
+    yield
+
+    os.environ.clear()
+    os.environ.update(original_environ)