More tests, not found page and dashboard fixes

When post was deleted, website shows a 404 page insead of an 500 page.
Also made the dashboard empty page message more explicit.

tests/api/admin_dashboard.rs

@@ -25,9 +25,32 @@ async fn logout_clears_session_state(connection_pool: PgPool) {
     assert!(html_page.contains("Connected as"));
     assert!(html_page.contains(&app.test_user.username));
 
-    let response = app.post_logout().await;
+    let response = app.logout().await;
     assert_is_redirect_to(&response, "/login");
 
     let response = app.get_admin_dashboard().await;
     assert_is_redirect_to(&response, "/login");
 }
+
+#[sqlx::test]
+async fn subscribers_are_visible_on_the_dashboard(connection_pool: PgPool) {
+    let app = TestApp::spawn(connection_pool).await;
+    app.admin_login().await;
+
+    let response = app.get_admin_dashboard_html().await;
+    assert!(response.contains("No data available"));
+
+    app.create_confirmed_subscriber().await;
+    let subscriber = sqlx::query!("SELECT id, email FROM subscriptions")
+        .fetch_one(&app.connection_pool)
+        .await
+        .unwrap();
+
+    let response = app.get_admin_dashboard_html().await;
+    assert!(response.contains(&subscriber.email));
+
+    app.delete_subscriber(subscriber.id).await;
+    let response = app.get_admin_dashboard_html().await;
+    assert!(response.contains("No data available"));
+    assert!(!response.contains(&subscriber.email));
+}