test: make the API-key fixture robust to empty-string env vars

A key left blank in a .env (var present but empty) bypassed the placeholder,
so local runs diverged from CI. Use 'or' instead of a .get default.

Author: Yijia-Xiao

tests/conftest.py

@@ -32,7 +32,9 @@ def pytest_configure(config):
 @pytest.fixture(autouse=True)
 def _dummy_api_keys(monkeypatch):
     for env_var in _API_KEY_ENV_VARS:
-        monkeypatch.setenv(env_var, os.environ.get(env_var, "placeholder"))
+        # `or` not a .get default: an env var present but empty (e.g. a key left
+        # blank in a .env copied from .env.example) must still get the placeholder.
+        monkeypatch.setenv(env_var, os.environ.get(env_var) or "placeholder")
 
 
 @pytest.fixture(autouse=True)