tests: ensure ephemeral config usage

Previously, pytest execution was influenced by poetry user
configuration. This change ensures that a new config.toml is used each
test case.

tests/conftest.py

@@ -99,6 +99,15 @@ def config(config_source, auth_config_source, mocker):
     return c
 
 
+@pytest.fixture(autouse=True)
+def mock_user_config_dir(mocker):
+    config_dir = tempfile.mkdtemp(prefix="poetry_config_")
+    mocker.patch("poetry.locations.CONFIG_DIR", new=config_dir)
+    mocker.patch("poetry.factory.CONFIG_DIR", new=config_dir)
+    yield
+    shutil.rmtree(config_dir, ignore_errors=True)
+
+
 @pytest.fixture(autouse=True)
 def download_mock(mocker):
     # Patch download to not download anything but to just copy from fixtures