fix test pollution due to changing os.environ

tests/conftest.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import os
 import sys
 
 from pathlib import Path
@@ -24,9 +25,12 @@
 from tests.helpers import PoetryTestApplication
 from tests.helpers import TestExecutor
 from tests.helpers import TestLocker
+from tests.helpers import isolated_environment
 
 
 if TYPE_CHECKING:
+    from collections.abc import Iterator
+
     from poetry.installation.executor import Executor
     from poetry.poetry import Poetry
     from poetry.utils.env import Env
@@ -102,6 +106,17 @@ def config(
     return c
 
 
+@pytest.fixture(autouse=True)
+def isolate_environ() -> Iterator[None]:
+    """Ensure the environment is isolated from user configuration."""
+    with isolated_environment():
+        for var in os.environ:
+            if var.startswith("POETRY_") or var in {"PYTHONPATH", "VIRTUAL_ENV"}:
+                del os.environ[var]
+
+        yield
+
+
 @pytest.fixture
 def fixture_root() -> Path:
     return Path(__file__).parent / "fixtures"

tests/helpers.py

@@ -1,5 +1,8 @@
 from __future__ import annotations
 
+import contextlib
+import os
+
 from typing import TYPE_CHECKING
 
 from poetry.console.application import Application
@@ -9,6 +12,7 @@
 
 
 if TYPE_CHECKING:
+    from collections.abc import Iterator
     from pathlib import Path
     from typing import Any
 
@@ -107,3 +111,21 @@ def _write_lock_data(self, data: TOMLDocument) -> None:
             return
 
         self._lock_data = data
+
+
+@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)

tests/test_helpers.py

@@ -0,0 +1,25 @@
+from __future__ import annotations
+
+import os
+
+from tests.helpers import isolated_environment
+
+
+def test_isolated_environment_restores_original_environ() -> None:
+    original_environ = dict(os.environ)
+    with isolated_environment():
+        os.environ["TEST_VAR"] = "test"
+    assert os.environ == original_environ
+
+
+def test_isolated_environment_clears_environ() -> None:
+    os.environ["TEST_VAR"] = "test"
+    with isolated_environment(clear=True):
+        assert "TEST_VAR" not in os.environ
+    assert "TEST_VAR" in os.environ
+
+
+def test_isolated_environment_updates_environ() -> None:
+    with isolated_environment(environ={"NEW_VAR": "new_value"}):
+        assert os.environ["NEW_VAR"] == "new_value"
+    assert "NEW_VAR" not in os.environ