Enforce objectives and controls have at least one element in everest …

…config

src/everest/config/everest_config.py

@@ -123,9 +123,10 @@ class EverestConfig(BaseModel):  # type: ignore
          Controls should have unique names each control defines
             a group of control variables
         """,
+        min_length=1,
     )
     objective_functions: list[ObjectiveFunctionConfig] = Field(
-        description="List of objective function specifications",
+        description="List of objective function specifications", min_length=1
     )
     optimization: OptimizationConfig | None = Field(
         default=OptimizationConfig(),
@@ -710,8 +711,17 @@ def with_defaults(cls, **kwargs):
         without having to provide empty defaults.
         """
         defaults = {
-            "controls": [],
-            "objective_functions": [],
+            "controls": [
+                {
+                    "name": "default_group",
+                    "type": "generic_control",
+                    "initial_guess": 0.5,
+                    "variables": [
+                        {"name": "default_name", "min": 0, "max": 1},
+                    ],
+                }
+            ],
+            "objective_functions": [{"name": "default"}],
             "config_path": ".",
             "model": {"realizations": [0]},
         }

tests/everest/test_config_validation.py

@@ -1025,3 +1025,54 @@ def test_load_file_with_errors(copy_math_func_test_data_to_tmp, capsys):
 
     assert "line: 16, column: 5" in captured.err
     assert "Extra inputs are not permitted (type=extra_forbidden)" in captured.err
+
+
+@pytest.mark.parametrize(
+    ["controls", "objectives", "error_msg"],
+    [
+        (
+            [],
+            [],
+            [
+                "controls\n  List should have at least 1 item after validation, not 0",
+                "objective_functions\n  List should have at least 1 item after validation, not 0",
+            ],
+        ),
+        (
+            [],
+            [{"name": "npv"}],
+            [
+                "controls\n  List should have at least 1 item after validation, not 0",
+            ],
+        ),
+        (
+            [
+                {
+                    "name": "test",
+                    "type": "generic_control",
+                    "initial_guess": 0.5,
+                    "variables": [
+                        {"name": "test", "min": 0, "max": 1},
+                    ],
+                }
+            ],
+            [{"name": "npv"}],
+            [],
+        ),
+    ],
+)
+def test_warning_empty_controls_and_objectives(controls, objectives, error_msg):
+    if error_msg:
+        with pytest.raises(ValueError) as e:
+            EverestConfig.with_defaults(
+                objective_functions=objectives,
+                controls=controls,
+            )
+
+        for msg in error_msg:
+            assert msg in str(e.value)
+    else:
+        EverestConfig.with_defaults(
+            objective_functions=objectives,
+            controls=controls,
+        )