Speed up unit tests (#2626)

* cache rule loader; skip rule tests on RL failure

-------
Co-authored-by: brokensound77 <brokensound77@users.noreply.github.com>

tests/base.py

@@ -5,26 +5,55 @@
 
 """Shared resources for tests."""
 
-import os
 import unittest
+from functools import lru_cache
 from typing import Union
 
 from detection_rules.rule import TOMLRule
 from detection_rules.rule_loader import DeprecatedCollection, DeprecatedRule, RuleCollection, production_filter
 
 
+@lru_cache
+def default_rules() -> RuleCollection:
+    return RuleCollection.default()
+
+
 class BaseRuleTest(unittest.TestCase):
     """Base class for shared test cases which need to load rules"""
 
+    RULE_LOADER_FAIL = False
+    RULE_LOADER_FAIL_MSG = None
+    RULE_LOADER_FAIL_RAISED = False
+
     @classmethod
     def setUpClass(cls):
-        os.environ["DR_NOTIFY_INTEGRATION_UPDATE_AVAILABLE"] = "1"
-        rc = RuleCollection.default()
-        cls.all_rules = rc.rules
-        cls.rule_lookup = rc.id_map
-        cls.production_rules = rc.filter(production_filter)
-        cls.deprecated_rules: DeprecatedCollection = rc.deprecated
+        # too noisy; refactor
+        # os.environ["DR_NOTIFY_INTEGRATION_UPDATE_AVAILABLE"] = "1"
+
+        if not cls.RULE_LOADER_FAIL:
+            try:
+                rc = default_rules()
+                cls.all_rules = rc.rules
+                cls.rule_lookup = rc.id_map
+                cls.production_rules = rc.filter(production_filter)
+                cls.deprecated_rules: DeprecatedCollection = rc.deprecated
+            except Exception as e:
+                cls.RULE_LOADER_FAIL = True
+                cls.RULE_LOADER_FAIL_MSG = str(e)
 
     @staticmethod
-    def rule_str(rule: Union[DeprecatedRule, TOMLRule], trailer=' ->'):
+    def rule_str(rule: Union[DeprecatedRule, TOMLRule], trailer=' ->') -> str:
         return f'{rule.id} - {rule.name}{trailer or ""}'
+
+    def setUp(self) -> None:
+        if self.RULE_LOADER_FAIL:
+            # limit the loader failure to just one run
+            # raise a dedicated test failure for the loader
+            if not self.RULE_LOADER_FAIL_RAISED:
+                self.RULE_LOADER_FAIL_RAISED = True
+                with self.subTest('Test that the rule loader loaded with no validation or other failures.'):
+                    self.fail(f'Rule loader failure: \n{self.RULE_LOADER_FAIL_MSG}')
+
+            self.skipTest('Rule loader failure')
+        else:
+            super().setUp()