tweak how config is initialized

Author: herin049

instrumentation/opentelemetry-instrumentation-system-metrics/src/opentelemetry/instrumentation/system_metrics/__init__.py

@@ -182,7 +182,7 @@ def __init__(
         config: dict[str, list[str] | None] | None = None,
     ):
         super().__init__()
-        self._config = config or _build_default_config()
+        self._config = _build_default_config() if config is None else config
         self._labels = {} if labels is None else labels
         self._meter = None
         self._python_implementation = python_implementation().lower()

instrumentation/opentelemetry-instrumentation-system-metrics/tests/test_system_metrics.py

@@ -1098,7 +1098,6 @@ def test_that_correct_config_is_read(self):
 
 class TestBuildDefaultConfig(unittest.TestCase):
     def setUp(self):
-        # Store original environment to restore after each test
         self.env_patcher = mock.patch.dict("os.environ", {}, clear=False)
         self.env_patcher.start()
 
@@ -1107,7 +1106,6 @@ def tearDown(self):
         os.environ.pop(OTEL_PYTHON_SYSTEM_METRICS_EXCLUDED_METRICS, None)
 
     def test_default_config_without_exclusions(self):
-        """Test that _DEFAULT_CONFIG is returned when no exclusions are specified."""
         test_cases = [
             {
                 "name": "no_env_var_set",