add unit test for endpoint resolution caching

tests/unit/test_endpoint_provider.py

@@ -14,6 +14,7 @@
 import json
 import logging
 import os
+import unittest
 
 import pytest
 
@@ -343,3 +344,24 @@ def test_ruleset_unknown_parameter_type_raises(partitions):
             partitions=partitions,
         )
     assert "Unknown parameter type: list." in str(exc_info.value)
+
+
+@pytest.fixture(scope="class")
+def test_endpoint_provider(endpoint_provider, request):
+    request.cls.endpoint_provider = endpoint_provider
+
+
+@pytest.mark.usefixtures("test_endpoint_provider")
+class EndpointProviderCacheTestCase(unittest.TestCase):
+    @unittest.mock.patch("botocore.endpoint_provider.RuleSet.evaluate")
+    def test_endpoint_resolution_caches(self, mock_evaluate):
+
+        for _ in range(5):
+            self.endpoint_provider.resolve_endpoint(**{"Region": "us-east-1"})
+        mock_evaluate.assert_called_once_with({"Region": "us-east-1"})
+        mock_evaluate.reset_mock()
+
+        regions = ["us-west-2", "us-west-1"]
+        for region in regions:
+            self.endpoint_provider.resolve_endpoint(**{"Region": region})
+        self.assertEqual(mock_evaluate.call_count, 2)