refactor cbc proxy and fix tests

moved the lambda invocation to a separate function to keep DRY

asserts on exception types need to be outside of with blocks, or they
won't trip (as the exception will stop execution of the inner with
block). the asserts were also the wrong way round so fixed that.

app/clients/cbc_proxy.py

@@ -20,6 +20,10 @@ import boto3
 #    the preceeding Alert message in the references field
 
 
+class CBCProxyException(Exception):
+    pass
+
+
 # Noop = no operation
 class CBCProxyNoopClient:
 
@@ -72,72 +76,53 @@ class CBCProxyClient:
             aws_secret_access_key=app.config['CBC_PROXY_AWS_SECRET_ACCESS_KEY'],
         )
 
-    def send_canary(
-        self,
-        identifier,
-    ):
-        payload_bytes = bytes(json.dumps({
-            'identifier': identifier,
-        }), encoding='utf8')
+    def _invoke_lambda(self, function_name, payload):
+        payload_bytes = bytes(json.dumps(payload), encoding='utf8')
 
         result = self._lambda_client.invoke(
-            FunctionName='canary',
+            FunctionName=function_name,
             InvocationType='RequestResponse',
             Payload=payload_bytes,
         )
 
         if result['StatusCode'] > 299:
-            raise Exception('Could not invoke lambda')
+            raise CBCProxyException('Could not invoke lambda')
 
         if 'FunctionError' in result:
-            raise Exception('Function exited with unhandled exception')
+            raise CBCProxyException('Function exited with unhandled exception')
+
+        return result
+
+    def send_canary(
+        self,
+        identifier,
+    ):
+        self._invoke_lambda(function_name='canary', payload={'identifier': identifier})
 
     def send_link_test(
         self,
         identifier,
     ):
-        payload_bytes = bytes(json.dumps({
-            'message_type': 'test',
-            'identifier': identifier,
-        }), encoding='utf8')
+        payload = {'message_type': 'test', 'identifier': identifier}
 
-        result = self._lambda_client.invoke(
-            FunctionName='bt-ee-1-proxy',
-            InvocationType='RequestResponse',
-            Payload=payload_bytes,
-        )
-
-        if result['StatusCode'] > 299:
-            raise Exception('Could not invoke lambda')
-
-        if 'FunctionError' in result:
-            raise Exception('Function exited with unhandled exception')
+        self._invoke_lambda(function_name='bt-ee-1-proxy', payload=payload)
 
     def create_and_send_broadcast(
         self,
         identifier, headline, description, areas,
         sent, expires,
     ):
-        payload_bytes = bytes(json.dumps({
+        payload = {
             'message_type': 'alert',
             'identifier': identifier,
             'headline': headline,
             'description': description,
             'areas': areas,
-            'sent': sent, 'expires': expires,
-        }), encoding='utf8')
+            'sent': sent,
+            'expires': expires,
+        }
 
-        result = self._lambda_client.invoke(
-            FunctionName='bt-ee-1-proxy',
-            InvocationType='RequestResponse',
-            Payload=payload_bytes,
-        )
-
-        if result['StatusCode'] > 299:
-            raise Exception('Could not invoke lambda')
-
-        if 'FunctionError' in result:
-            raise Exception('Function exited with unhandled exception')
+        self._invoke_lambda(function_name='bt-ee-1-proxy', payload=payload)
 
     # We have not implementated updating a broadcast
     def update_and_send_broadcast(