For the purpose of our tests, we will keep the new transaction relatively simple: our transaction will merge two assets into one, adding their value in the process.

To declare the new transaction, we will edit the model file and add this new declaration:

transaction MergeAssets {
--> Asset mergeFrom
--> Asset mergeTo
}

With the definition created, let's add the logic in the /lib/logic.js file:

/**
  * Sample transaction
  * @param {org.example.biznet.MergeAssets} tx
  * @transaction
  */
function onMergeAssets(tx) {
  var assetRegistry;
  var mergeFromAsset = tx.mergeFrom;
  var mergeToAsset = tx.mergeTo;
  mergeToAsset.value += tx.mergeFrom.value;

  return getAssetRegistry('org.example.biznet.SampleAsset')
    .then(function(ar) {
      assetRegistry = ar;
      return assetRegistry.update(mergeToAsset);
    })
    .then(function() {
      return assetRegistry.remove(mergeFromAsset);
    });
}

That's all there is to it! Of course, some may remark that we are not following a good methodology—where are our unit tests for this code? Let's proceed. Don't worry, it's all part of the plan!