Handler to send emails to confirmed subscribers

tests/api/subscriptions.rs

@@ -81,7 +81,7 @@ async fn subscribe_returns_a_400_when_fields_are_present_but_invalid() {
         assert_eq!(
             400,
             response.status().as_u16(),
-            "the API did not return a 400 Bad Request when the payload had an {}.",
+            "the API did not fail with 400 Bad Request when the payload had an {}.",
             description
         );
     }