Explicitly set the environment defaults in settings.py

kedro/framework/session/session.py

@@ -253,11 +253,16 @@ def _get_config_loader(self) -> AbstractConfigLoader:
         extra_params = self.store.get("extra_params")
 
         config_loader_class = settings.CONFIG_LOADER_CLASS
+        config_loader_args = settings.CONFIG_LOADER_ARGS
+        if not (
+            "base_env" in config_loader_args or "default_run_env" in config_loader_args
+        ):
+            config_loader_args.update({"base_env": "base", "default_run_env": "local"})
         return config_loader_class(
             conf_source=self._conf_source,
             env=env,
             runtime_params=extra_params,
-            **settings.CONFIG_LOADER_ARGS,
+            **config_loader_args,
         )
 
     def close(self):

tests/framework/session/test_session.py

@@ -165,6 +165,17 @@ class MockSettings(_ProjectSettings):
     return _mock_imported_settings_paths(mocker, MockSettings())
 
 
+@pytest.fixture
+def mock_settings_config_loader_args_env(mocker):
+    class MockSettings(_ProjectSettings):
+        _CONFIG_LOADER_ARGS = Validator(
+            "CONFIG_LOADER_ARGS",
+            default={"base_env": "something_new"},
+        )
+
+    return _mock_imported_settings_paths(mocker, MockSettings())
+
+
 @pytest.fixture
 def mock_settings_file_bad_config_loader_class(tmpdir):
     mock_settings_file = tmpdir.join("mock_settings_file.py")
@@ -423,6 +434,28 @@ def test_load_config_loader_args(self, fake_project, mock_package_name, mocker):
         )
         assert result["spark"] == ["spark/*"]
 
+    @pytest.mark.usefixtures("mock_settings_config_loader_args")
+    def test_config_loader_args_dont_overwrite_env(
+        self, fake_project, mock_package_name, mocker
+    ):
+        session = KedroSession.create(mock_package_name, fake_project)
+        result = session._get_config_loader()
+
+        assert isinstance(result, OmegaConfigLoader)
+        assert result.base_env == "base"
+        assert result.default_run_env == "local"
+
+    @pytest.mark.usefixtures("mock_settings_config_loader_args_env")
+    def test_config_loader_args_overwrite_env(
+        self, fake_project, mock_package_name, mocker
+    ):
+        session = KedroSession.create(mock_package_name, fake_project)
+        result = session._get_config_loader()
+
+        assert isinstance(result, OmegaConfigLoader)
+        assert result.base_env == "something_new"
+        assert result.default_run_env == ""
+
     def test_broken_config_loader(self, mock_settings_file_bad_config_loader_class):
         pattern = (
             "Invalid value 'tests.framework.session.test_session.BadConfigLoader' received "