[DBMON-6334] Add ClickHouse unit tests to track all config default value changes

clickhouse/tests/test_config_defaults.py

@@ -0,0 +1,189 @@
+# (C) Datadog, Inc. 2026-present
+# All rights reserved
+# Licensed under a 3-clause BSD style license (see LICENSE)
+
+"""
+The goal of these tests is to verify our default configuration values are correct and remain consistent.
+Failing tests indicate a regression in our defaults and should be inspected carefully.
+Default values are duplicated within this file by design to ensure tests fail if the value changes unexpectedly.
+"""
+
+import pytest
+
+from datadog_checks.clickhouse import ClickhouseCheck
+from datadog_checks.clickhouse.config_models.instance import InstanceConfig
+
+EXPECTED_DEFAULTS = {
+    # === Required fields (no defaults) ===
+    'server': None,
+    # === Connection configuration ===
+    'port': 8123,
+    'db': 'default',
+    'username': 'default',
+    'password': '',
+    'connect_timeout': 10,
+    'read_timeout': 10,
+    'compression': None,
+    'tls_verify': False,
+    'tls_ca_cert': None,
+    'verify': True,
+    # === Database identifier ===
+    'database_identifier': {
+        'template': '$server:$port:$db',
+    },
+    # === DBM toggle ===
+    'dbm': False,
+    'single_endpoint_mode': False,
+    # === DBM: Query metrics ===
+    'query_metrics': {
+        'enabled': True,
+        'collection_interval': 10,
+        'run_sync': False,
+        'full_statement_text_cache_max_size': 10000,
+        'full_statement_text_samples_per_hour_per_query': 1,
+    },
+    # === DBM: Query samples ===
+    'query_samples': {
+        'enabled': True,
+        'collection_interval': 1,
+        'payload_row_limit': 1000,
+        'run_sync': False,
+    },
+    # === DBM: Query completions ===
+    'query_completions': {
+        'enabled': True,
+        'collection_interval': 10,
+        'samples_per_hour_per_query': 15,
+        'seen_samples_cache_maxsize': 10000,
+        'max_samples_per_collection': 1000,
+        'run_sync': False,
+    },
+    # === Tagging ===
+    'tags': (),
+    'disable_generic_tags': False,
+    'enable_legacy_tags_normalization': True,
+    # === Custom queries ===
+    'custom_queries': None,
+    'only_custom_queries': False,
+    'use_global_custom_queries': 'true',
+    # === Agent standard fields ===
+    'min_collection_interval': 15,
+    'empty_default_hostname': False,
+    # === User-provided / no default ===
+    'service': None,
+    'metric_patterns': None,
+}
+
+pytestmark = pytest.mark.unit
+
+
+@pytest.fixture
+def minimal_instance():
+    """Minimal instance configuration with only the required field."""
+    return {'server': 'localhost'}
+
+
+def test_all_config_defaults(minimal_instance):
+    """
+    Verify that all InstanceConfig fields have the expected default values when only
+    the required 'server' field is provided.
+
+    If a field is missing from EXPECTED_DEFAULTS the test fails with instructions on how to fix it.
+    Failures on existing fields indicate a potential config regression for existing users.
+    """
+    check = ClickhouseCheck('clickhouse', {}, [minimal_instance])
+    config = check._config
+
+    all_fields = set(InstanceConfig.__annotations__.keys())
+
+    missing_from_expected = all_fields - set(EXPECTED_DEFAULTS.keys())
+    if missing_from_expected:
+        pytest.fail(
+            f"\n\n{'=' * 80}\n"
+            f"MISSING EXPECTED DEFAULTS!\n"
+            f"{'=' * 80}\n\n"
+            f"The following fields exist in InstanceConfig but are missing from EXPECTED_DEFAULTS:\n"
+            f"  {sorted(missing_from_expected)}\n\n"
+            f"To fix this, add each field to EXPECTED_DEFAULTS in test_config_defaults.py\n"
+            f"with its expected default value. Examples:\n"
+            f"  - Simple field:   'field_name': default_value,\n"
+            f"  - No default:     'field_name': None,\n"
+            f"  - Nested object:  'field_name': {{'key': 'value'}},\n"
+            f"{'=' * 80}\n"
+        )
+
+    extra_in_expected = set(EXPECTED_DEFAULTS.keys()) - all_fields
+    if extra_in_expected:
+        pytest.fail(
+            f"\n\nThe following fields are in EXPECTED_DEFAULTS but don't exist in InstanceConfig:\n"
+            f"  {sorted(extra_in_expected)}\n"
+            f"Remove them from EXPECTED_DEFAULTS in test_config_defaults.py."
+        )
+
+    failures = []
+
+    for field_name, expected_value in EXPECTED_DEFAULTS.items():
+        if field_name == 'server':
+            continue
+
+        actual_value = getattr(config, field_name)
+
+        if isinstance(expected_value, dict):
+            _compare_nested_object(actual_value, expected_value, field_name, failures)
+        elif isinstance(expected_value, (list, tuple)):
+            if isinstance(actual_value, (list, tuple)):
+                if type(expected_value)(actual_value) != expected_value:
+                    failures.append(f"{field_name}: expected {expected_value!r}, got {actual_value!r}")
+            elif actual_value is None:
+                failures.append(f"{field_name}: expected {expected_value!r}, got None")
+            else:
+                failures.append(f"{field_name}: expected {expected_value!r}, got {actual_value!r}")
+        else:
+            if actual_value != expected_value:
+                failures.append(f"{field_name}: expected {expected_value!r}, got {actual_value!r}")
+
+    if failures:
+        pytest.fail(
+            f"\n\n{'=' * 80}\n"
+            f"DEFAULT VALUE MISMATCHES DETECTED!\n"
+            f"{'=' * 80}\n\n"
+            f"The following fields have unexpected default values:\n\n"
+            + "\n".join(f"  • {f}" for f in failures)
+            + f"\n\n"
+            f"This indicates either:\n"
+            f"  1. A regression in default values (BAD — investigate carefully!)\n"
+            f"  2. EXPECTED_DEFAULTS needs updating to reflect intentional new behaviour\n"
+            f"{'=' * 80}\n"
+        )
+
+
+def _compare_nested_object(actual_obj, expected_dict, field_path, failures):
+    """Recursively compare a nested config object against an expected dict."""
+    actual_fields = set(type(actual_obj).model_fields.keys())
+    expected_fields = set(expected_dict.keys())
+    missing = actual_fields - expected_fields
+    if missing:
+        failures.append(
+            f"{field_path}: nested fields exist in model but are missing from EXPECTED_DEFAULTS: {sorted(missing)}"
+        )
+
+    for key, expected_value in expected_dict.items():
+        try:
+            actual_value = getattr(actual_obj, key)
+        except AttributeError:
+            failures.append(f"{field_path}.{key}: field not accessible on config object")
+            continue
+
+        if isinstance(expected_value, dict):
+            _compare_nested_object(actual_value, expected_value, f"{field_path}.{key}", failures)
+        elif isinstance(expected_value, (list, tuple)):
+            if isinstance(actual_value, (list, tuple)):
+                if type(expected_value)(actual_value) != expected_value:
+                    failures.append(f"{field_path}.{key}: expected {expected_value!r}, got {actual_value!r}")
+            elif actual_value is None:
+                failures.append(f"{field_path}.{key}: expected {expected_value!r}, got None")
+            else:
+                failures.append(f"{field_path}.{key}: expected {expected_value!r}, got {actual_value!r}")
+        else:
+            if actual_value != expected_value:
+                failures.append(f"{field_path}.{key}: expected {expected_value!r}, got {actual_value!r}")