fix(python-helpers): honor environment configuration precedence

src/libraries/python/nv-cloud-function-helpers/AGENTS.md

@@ -32,5 +32,11 @@ Declared in `setup.py`:
 
 ## Tests
 
-No test suite is present yet. Add pytest coverage alongside changes when
-modifying helpers.
+Run the helper tests from this directory with pytest installed:
+
+```sh
+python3 -m pytest -q tests
+```
+
+Add regression coverage alongside helper changes. Tests use local fixtures and
+do not need a running Triton or NVCF service.

src/libraries/python/nv-cloud-function-helpers/nv_cloud_function_helpers/nvcf_container/helpers.py

@@ -169,12 +169,9 @@ def get_config_value(value_name: str, model_config: dict = None) -> str:
     """
     returns a value from Triton's model config or from environment variable with the priority given to the environment
     """
-    if model_config is None:
+    if model_config is None or value_name in os.environ:
         return os.environ[value_name]
-    else:
-        return os.environ.get(
-            value_name, model_config["parameters"][value_name]["string_value"]
-        )
+    return model_config["parameters"][value_name]["string_value"]
 
 
 def load_image(input_str: str, root_dir: str, has_transparency: bool = False):

src/libraries/python/nv-cloud-function-helpers/tests/test_config_value.py

@@ -0,0 +1,97 @@
+# SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+# SPDX-License-Identifier: Apache-2.0
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Environment settings take precedence without evaluating unused fallbacks."""
+
+from copy import deepcopy
+
+import pytest
+
+from nv_cloud_function_helpers.nvcf_container.helpers import get_config_value
+
+KEY = "NVCF_TEST_CONFIG_OVERRIDE"
+
+
+@pytest.mark.parametrize("environment_value", ["configured", ""])
+@pytest.mark.parametrize(
+    "config",
+    [
+        None,
+        {},
+        {"parameters": {}},
+        {"parameters": {KEY: {}}},
+        {"parameters": {KEY: {"string_value": "fallback"}}},
+    ],
+)
+def test_environment_wins_even_without_model_fallback(
+    monkeypatch, environment_value, config
+):
+    monkeypatch.setenv(KEY, environment_value)
+    before = deepcopy(config)
+    assert get_config_value(KEY, config) == environment_value
+    assert config == before
+
+
+@pytest.mark.parametrize("model_value", ["fallback", "", "0"])
+def test_model_value_is_used_when_environment_is_absent(
+    monkeypatch, model_value
+):
+    monkeypatch.delenv(KEY, raising=False)
+    config = {"parameters": {KEY: {"string_value": model_value}}}
+    before = deepcopy(config)
+    assert get_config_value(KEY, config) == model_value
+    assert config == before
+
+
+@pytest.mark.parametrize(
+    "config, missing_key",
+    [
+        (None, KEY),
+        ({}, "parameters"),
+        ({"parameters": {}}, KEY),
+        ({"parameters": {KEY: {}}}, "string_value"),
+    ],
+)
+def test_missing_values_keep_their_key_errors(monkeypatch, config, missing_key):
+    monkeypatch.delenv(KEY, raising=False)
+    with pytest.raises(KeyError) as error:
+        get_config_value(KEY, config)
+    assert error.value.args == (missing_key,)
+
+
+def test_unused_fallback_is_not_read(monkeypatch):
+    class UnreadableConfig(dict):
+        def __getitem__(self, key):
+            raise AssertionError("Environment override must not read fallback")
+
+    monkeypatch.setenv(KEY, "override")
+    assert get_config_value(KEY, UnreadableConfig()) == "override"
+
+
+def test_environment_changes_are_not_cached(monkeypatch):
+    config = {"parameters": {KEY: {"string_value": "fallback"}}}
+    monkeypatch.setenv(KEY, "first")
+    assert get_config_value(KEY, config) == "first"
+    monkeypatch.setenv(KEY, "second")
+    assert get_config_value(KEY, config) == "second"
+    monkeypatch.delenv(KEY)
+    assert get_config_value(KEY, config) == "fallback"
+
+
+def test_unrelated_environment_value_does_not_override(monkeypatch):
+    monkeypatch.delenv(KEY, raising=False)
+    monkeypatch.setenv(KEY + "_OTHER", "different")
+    config = {"parameters": {KEY: {"string_value": "fallback"}}}
+    assert get_config_value(KEY, config) == "fallback"