Make use of find_all in the read test

atmosphere-core/src/testing.rs

@@ -59,13 +59,20 @@ where
         "instance was found (find_optional) after deletion"
     );
 
+    assert!(
+        E::find_all(pool).await.unwrap().is_empty(),
+        "there was an instance found in the database before creating"
+    );
+
     instance.create(pool).await.expect("insertion did not work");
 
     let retrieved = E::find(instance.pk(), pool)
         .await
         .expect("instance not found after insertion");
 
     assert_eq!(instance, retrieved);
+
+    assert_eq!(E::find_all(pool).await.unwrap(), vec![instance.clone()]);
 }
 
 /// Tests updating of an entity in the database.