Use the crate mockall to mock the email service in integration tests

backend/tests/utils/mock_email.rs

@@ -1,23 +1,20 @@
 use std::sync::Arc;
 
-use recipes::email;
+use async_trait::async_trait;
+use mockall::{mock, predicate::*};
 
-pub struct MockEmailService;
+use crate::email;
 
-impl MockEmailService {
-    pub fn create_service() -> Arc<dyn email::EmailServiceTrait> {
-        Arc::new(Self {})
+mock! {
+    pub EmailService {}
+    #[async_trait]
+    impl email::EmailServiceTrait for EmailService {
+        async fn send_email(&self, email: &str, title: &str, message: &str)
+            -> Result<(), email::Error>;
     }
 }
 
-#[async_trait::async_trait]
-impl email::EmailServiceTrait for MockEmailService {
-    async fn send_email(
-        &self,
-        _email: &str,
-        _title: &str,
-        _message: &str,
-    ) -> Result<(), email::Error> {
-        Ok(())
-    }
+// Default email service: will crash if `send_email` method is called.
+pub fn new_mock_email_service() -> Arc<dyn email::EmailServiceTrait> {
+    Arc::new(MockEmailService::new())
 }