custom linter rules test: Load rules in test setup.

tools/tests/test_linter_custom_check.py

@@ -4,16 +4,19 @@ from itertools import chain
 from mock import patch, MagicMock
 from unittest import TestCase
 
+from typing import Any, Dict, List
+
 from tools.linter_lib.custom_check import build_custom_checkers
 
 ROOT_DIR = os.path.abspath(os.path.join(__file__, '..', '..', '..'))
 CHECK_MESSAGE = "Fix the corresponding rule in `tools/linter_lib/custom_check.py`."
 
-@patch('tools.linter_lib.custom_check.custom_check_file', return_value=False)
 class TestCustomRulesFormat(TestCase):
-    def test_paths_in_rules(self, mock_custom_check_file):
-        # type: (MagicMock) -> None
-        """Verifies that the paths mentioned in linter rules actually exist"""
+
+    def setUp(self):
+        # type: () -> None
+        self.all_rules = []  # type: List[Dict[str, Any]]
+        with patch('tools.linter_lib.custom_check.custom_check_file', return_value=False) as mock_custom_check_file:
             by_lang = dict.fromkeys(['py', 'js', 'sh', 'css', 'handlebars', 'html', 'json', 'md', 'txt', 'text', 'yaml'],
                                     ['foo/bar.baz'])
             check_custom_checks_py, check_custom_checks_nonpy = build_custom_checkers(by_lang)
@@ -21,7 +24,12 @@ class TestCustomRulesFormat(TestCase):
             check_custom_checks_nonpy()
             for call_args in mock_custom_check_file.call_args_list:
                 rule_set = call_args[0][2]
-            for rule in rule_set:
+                self.all_rules.extend(rule_set)
+
+    def test_paths_in_rules(self):
+        # type: () -> None
+        """Verifies that the paths mentioned in linter rules actually exist"""
+        for rule in self.all_rules:
             for path in rule.get('exclude', {}):
                 abs_path = os.path.abspath(os.path.join(ROOT_DIR, path))
                 self.assertTrue(os.path.exists(abs_path),