WIP: Attempt at setting up old storage items before migration tests

WARNING: adds an assert inside v1::migrate() which should be removed!

pallets/bridge/src/migrations/mod.rs

@@ -35,13 +35,28 @@ pub(crate) fn migrate<T: Config>() -> Weight {
 #[cfg(test)]
 pub mod tests {
     use super::{migrate, Weight};
-    use crate::mock::{ExtBuilder, Test};
+    use crate::{
+        mock::{ExtBuilder, Test},
+        Authorities,
+    };
+    use frame_support::{storage::unhashed, StoragePrefixedMap};
+    use sp_io::hashing::twox_128;
 
     #[test]
     fn migrate_should_not_crash() {
         ExtBuilder.build_and_execute(|| {
-            let weight = migrate::<Test>();
+            // simulate an environment where the old "bridge" pallet has some items in storage
+            // before we apply the migrations
+            let authority = b"authority";
+
+            let authorities_prefix = [
+                &twox_128(b"bridge"),
+                &twox_128(Authorities::<Test>::storage_prefix())[..],
+            ]
+            .concat();
+            unhashed::put_raw(&authorities_prefix, authority);
 
+            let weight = migrate::<Test>();
             assert_ne!(weight, Weight::zero());
         });
     }

pallets/bridge/src/migrations/v1.rs

@@ -48,6 +48,7 @@ impl<T: Config> Migrate for Migration<T> {
         }
 
         let old_count = count_storage_items(OLD_PALLET_NAME);
+        assert_ne!(old_count, 0, "Old pallet storage must not be empty");
 
         move_pallet(OLD_PALLET_NAME.as_bytes(), new_pallet_name.as_bytes());