env: installing into `MockEnv` should not have side effects on another env (#7141)

MockEnv should not use paths of SystemEnv for paths that may be written to

src/poetry/utils/env.py

@@ -2039,6 +2039,17 @@ class MockEnv(NullEnv):
 
 
         return self._sys_path
         return self._sys_path
 
 
+    @property
+    def paths(self) -> dict[str, str]:
+        if self._paths is None:
+            self._paths = self.get_paths()
+            self._paths["platlib"] = str(self._path / "platlib")
+            self._paths["purelib"] = str(self._path / "purelib")
+            self._paths["scripts"] = str(self._path / "scripts")
+            self._paths["data"] = str(self._path / "data")
+
+        return self._paths
+
     def get_marker_env(self) -> dict[str, Any]:
     def get_marker_env(self) -> dict[str, Any]:
         if self._mock_marker_env is not None:
         if self._mock_marker_env is not None:
             return self._mock_marker_env
             return self._mock_marker_env

tests/masonry/builders/test_editable_builder.py

@@ -291,16 +291,6 @@ def test_builder_should_execute_build_scripts(
     mocker: MockerFixture, extended_without_setup_poetry: Poetry, tmp_path: Path
     mocker: MockerFixture, extended_without_setup_poetry: Poetry, tmp_path: Path
 ):
 ):
     env = MockEnv(path=tmp_path / "foo")
     env = MockEnv(path=tmp_path / "foo")
-    site_packages_dir = tmp_path / "site-packages"
-    site_packages_dir.mkdir(parents=True, exist_ok=True)
-    mocker.patch.object(
-        env,
-        "get_paths",
-        return_value={
-            "purelib": str(site_packages_dir),
-            "platlib": str(site_packages_dir),
-        },
-    )
     mocker.patch(
     mocker.patch(
         "poetry.masonry.builders.editable.build_environment"
         "poetry.masonry.builders.editable.build_environment"
     ).return_value.__enter__.return_value = env
     ).return_value.__enter__.return_value = env