message: add scratch.read to test
diff: @@ -495,19 +495,19 @@ mod tests {
  .commit(correlation_id, updated_hash, add_effects)
  .unwrap();
  + let scratch_checkout = scratch.checkout(root_hash).unwrap().unwrap();
  let updated_checkout = state2.checkout(updated_hash).unwrap().unwrap();
  let all_keys = updated_checkout
  .keys_with_prefix(correlation_id, &[])
  .unwrap();
  - let stored_values = scratch.into_inner();
  - assert_eq!(all_keys.len(), stored_values.len());
  -
  // Check that cache matches the contents of the second instance of lmdb
  for key in all_keys {
  - assert!(stored_values.get(&key).is_some());
  assert_eq!(
  - stored_values.get(&key),
  + scratch_checkout
  + .read(correlation_id, &key)
  + .unwrap()
  + .as_ref(),
  updated_checkout
  .read(correlation_id, &key)
  .unwrap()
  