catch boto exceptions

these will happen if, for example, you have issues connecting to AWS or
permission issues.

Still failover if we get one of these exceptions, as I think it might be
possible to have a problem only related to one of the lambdas.

tests/app/clients/test_cbc_proxy.py

@@ -4,6 +4,7 @@ from collections import namedtuple
 from datetime import datetime
 from unittest.mock import Mock, call
 
+from botocore.exceptions import ClientError as BotoClientError
 import pytest
 
 from app.clients.cbc_proxy import (
@@ -316,6 +317,50 @@ def test_cbc_proxy_vodafone_cancel_invokes_function(mocker, cbc_proxy_vodafone):
     assert payload['sent'] == sent
 
 
+@pytest.mark.parametrize('cbc', ['ee', 'vodafone', 'three', 'o2'])
+def test_cbc_proxy_will_failover_to_second_lambda_if_boto_client_error(
+    mocker,
+    cbc_proxy_client,
+    cbc
+):
+    cbc_proxy = cbc_proxy_client.get_proxy(cbc)
+
+    ld_client_mock = mocker.patch.object(
+        cbc_proxy,
+        '_lambda_client',
+        create=True,
+    )
+
+    ld_client_mock.invoke.side_effect = BotoClientError({}, 'error')
+
+    with pytest.raises(CBCProxyRetryableException) as e:
+        cbc_proxy.create_and_send_broadcast(
+            identifier='my-identifier',
+            message_number='0000007b',
+            headline='my-headline',
+            description='test-description',
+            areas=EXAMPLE_AREAS,
+            sent='a-passed-through-sent-value',
+            expires='a-passed-through-expires-value',
+            channel="severe",
+        )
+
+    assert e.match(f'Lambda failed for both {cbc}-1-proxy and {cbc}-2-proxy')
+
+    assert ld_client_mock.invoke.call_args_list == [
+        call(
+            FunctionName=f'{cbc}-1-proxy',
+            InvocationType='RequestResponse',
+            Payload=mocker.ANY,
+        ),
+        call(
+            FunctionName=f'{cbc}-2-proxy',
+            InvocationType='RequestResponse',
+            Payload=mocker.ANY,
+        )
+    ]
+
+
 @pytest.mark.parametrize('cbc', ['ee', 'vodafone', 'three', 'o2'])
 def test_cbc_proxy_will_failover_to_second_lambda_if_function_error(
     mocker,