diff --git a/tests/conftest.py b/tests/conftest.py
index 6dee1e1b032..5515651419a 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -34,6 +34,7 @@
 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(cls: PackageInfo, path: Path) -> PackageInfo:
 
 @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)
diff --git a/tests/helpers.py b/tests/helpers.py
index 9992c0e83dc..1969873263b 100644
--- a/tests/helpers.py
+++ b/tests/helpers.py
@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import contextlib
 import os
 import re
 import shutil
@@ -9,6 +10,7 @@
 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 @@ def find_links_for_package(self, package: Package) -> list[Link]:
                 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)