Fix a missing edge case for no error handler, add tests

The error handler behavior descended down through the connection management part of the code and that was missed, this covers that.
Add test coverage for the new branches

sprockets_postgres.py

@@ -373,7 +373,10 @@ class ApplicationMixin:
                                     _attempt + 1) as connector:
                                 yield connector
                             return
-            exc = on_error('postgres_connector', ConnectionException(str(err)))
+            if on_error is None:
+                raise ConnectionException(str(err))
+            exc = on_error(
+                'postgres_connector', ConnectionException(str(err)))
             if exc:
                 raise exc
             else:  # postgres_status.on_error does not return an exception

tests.py

@@ -168,6 +168,18 @@ class NoErrorRequestHandler(ErrorRequestHandler):
         return None
 
 
+class NoMixinRequestHandler(web.RequestHandler):
+
+    async def get(self):
+        try:
+            async with self.application.postgres_connector() as connector:
+                await connector.execute('SELECT 1', {})
+        except sprockets_postgres.ConnectionException:
+            raise web.HTTPError(503)
+        else:
+            raise web.HTTPError(418)
+
+
 class NoRowRequestHandler(RequestHandler):
 
     GET_SQL = """\
@@ -257,7 +269,7 @@ class UnhandledExceptionRequestHandler(RequestHandler):
             await self.postgres_execute(self.GET_SQL)
         except psycopg2.DataError:
             raise web.HTTPError(422)
-        raise web.HTTPError(500, 'This should have failed')
+        raise web.HTTPError(418, 'This should have failed')
 
     def on_postgres_error(self,
                           metric_name: str,
@@ -271,6 +283,14 @@ class UnhandledExceptionRequestHandler(RequestHandler):
         return exc
 
 
+class DontRaiseRequestHandler(UnhandledExceptionRequestHandler):
+
+    def on_postgres_error(self,
+                          metric_name: str,
+                          exc: Exception) -> typing.Optional[Exception]:
+        return None
+
+
 class Application(sprockets_postgres.ApplicationMixin,
                   app.Application):
 
@@ -303,6 +323,7 @@ class TestCase(testing.SprocketsHttpTestCase):
         self.app = Application(handlers=[
             web.url('/callproc', CallprocRequestHandler),
             web.url('/count', CountRequestHandler),
+            web.url('/dont-raise', DontRaiseRequestHandler),
             web.url('/error', ErrorRequestHandler),
             web.url('/error-passthrough', ErrorPassthroughRequestHandler),
             web.url('/execute', ExecuteRequestHandler),
@@ -310,6 +331,7 @@ class TestCase(testing.SprocketsHttpTestCase):
             web.url('/metrics-mixin', MetricsMixinRequestHandler),
             web.url('/multi-row', MultiRowRequestHandler),
             web.url('/no-error', NoErrorRequestHandler),
+            web.url('/no-mixin', NoMixinRequestHandler),
             web.url('/no-row', NoRowRequestHandler),
             web.url('/pdexecute', ProblemDetailsExecuteRequestHandler),
             web.url('/row-count-no-rows', RowCountNoRowsRequestHandler),
@@ -529,7 +551,7 @@ class RequestHandlerMixinTestCase(TestCase):
         self.assertIsNone(json.loads(response.body)['value'])
 
 
-class RequestHandlerMixinHTTPErrorTestCase(TestCase):
+class HTTPErrorTestCase(TestCase):
 
     def setUp(self):
         super().setUp()
@@ -574,6 +596,25 @@ class RequestHandlerMixinHTTPErrorTestCase(TestCase):
         response = self.fetch('/execute?value=1')
         self.assertEqual(response.code, 503)
 
+    def test_on_error_no_exception_branch(self):
+        response = self.fetch('/dont-raise')
+        self.assertEqual(response.code, 418)
+
+
+class NoMixinTestCase(TestCase):
+
+    @mock.patch('aiopg.cursor.Cursor.execute')
+    def test_postgres_cursor_raises(self, execute):
+        execute.side_effect = psycopg2.ProgrammingError()
+        response = self.fetch('/no-mixin')
+        self.assertEqual(response.code, 500)
+
+    @mock.patch('aiopg.pool.Pool.acquire')
+    def test_postgres_status_connect_error(self, acquire):
+        acquire.side_effect = asyncio.TimeoutError()
+        response = self.fetch('/no-mixin')
+        self.assertEqual(response.code, 503)
+
 
 class TransactionTestCase(TestCase):