tests: verify correction works

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

nox/sessions.py

@@ -41,7 +41,7 @@
 import nox.virtualenv
 from nox._decorators import Func
 from nox.logger import logger
-from nox.virtualenv import UV, CondaEnv, PassthroughEnv, ProcessEnv, VirtualEnv
+from nox.virtualenv import CondaEnv, PassthroughEnv, ProcessEnv, VirtualEnv
 
 if TYPE_CHECKING:
     from nox.manifest import Manifest
@@ -500,8 +500,8 @@ def _run(
             return self._run_func(args[0], args[1:], kwargs)  # type: ignore[unreachable]
 
         # Using `"uv"` when `uv` is the backend is guaranteed to work, even if it was co-installed with nox.
-        if self.virtualenv.venv_backend == "uv" and args[0] == "uv" and UV != "uv":
-            args = (UV, *args[1:])
+        if self.virtualenv.venv_backend == "uv" and args[0] == "uv" and nox.virtualenv.UV != "uv":
+            args = (nox.virualenv.UV, *args[1:])
 
         # Combine the env argument with our virtualenv's env vars.
         if include_outer_env:

tests/test_sessions.py

@@ -823,7 +823,8 @@ def test_session_venv_reused_with_no_install(self, no_install, reused, run_calle
 
         assert run.called is run_called
 
-    def test_install_uv(self):
+    @pytest.mark.parametrize("uv", [None, "/some/uv"])
+    def test_install_uv(self, uv, monkeypatch):
         runner = nox.sessions.SessionRunner(
             name="test",
             signatures=["test"],
@@ -840,6 +841,9 @@ class SessionNoSlots(nox.sessions.Session):
 
         session = SessionNoSlots(runner=runner)
 
+        if uv is not None:
+            monkeypatch.setattr(nox.virtualenv, "UV", uv)
+
         with mock.patch.object(session, "_run", autospec=True) as run:
             session.install("requests", "urllib3", silent=False)
             run.assert_called_once_with(