Add test to detect drift in expected optimized platforms

In the documentation, we document which instance types use the CRT
S3 client when in ``auto`` mode. This test ensures when we update
the CRT, we are alerted of any changes to optimized platforms and
subsequently update the ``auto`` preferred client documentation.

tests/unit/customizations/s3/test_factory.py

@@ -10,6 +10,7 @@
 # distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF
 # ANY KIND, either express or implied. See the License for the specific
 # language governing permissions and limitations under the License.
+import awscrt.s3
 import pytest
 from awscli.testutils import unittest, mock, FileCreator
 
@@ -70,6 +71,25 @@ def s3_params():
     }
 
 
+def test_crt_get_optimized_platforms_match_expected_platforms():
+    expected_platforms = {
+        'p4d.24xlarge',
+        'p4de.24xlarge',
+        'p5.48xlarge',
+        'trn1n.32xlarge',
+        'trn1.32xlarge',
+    }
+    actual_platforms = set(awscrt.s3.get_optimized_platforms())
+    assert expected_platforms == actual_platforms, (
+        'Expected set of CRT optimized platforms does not match result from '
+        'CRT. The result from CRT determines which platforms the CLI will '
+        'automatically use the S3 CRT client for. If the change in optimized '
+        'platforms is expected/appropriate, update the expected_platforms '
+        'set in this test and the list of CRT optimized platforms in the '
+        'documentation located at: awscli/topics/s3-config.rst'
+    )
+
+
 class TestClientFactory(unittest.TestCase):
     def setUp(self):
         self.session = mock.Mock(Session)