CU-86dtu92vq - Include how to test smart contract events using boa te…

…st constructor

docs/source/testing-and-debugging.md

@@ -135,3 +135,35 @@ of the transaction.
         result, _ = await self.call("get_message", return_type=str)
         self.assertEqual(new_message, result)
 ```
+
+#### Accessing Events
+
+If you want to test events, you'll get all the notifications that were emitted on the transaction from the second return
+value of the `call` method. The resulting stack of every notification is a list of stack items, so it's best you unwrap
+them using [neo-mamba unwrapping methods](https://dojo.coz.io/neo3/mamba/api/neo3/api/helpers/unwrap.html). In this
+example, we are testing the "Transfer" event, so we can use the `Nep17TransferEvent` class from `boaconstructor`. If you
+plan to test other events, it's best you also create a class or method that will help you unwrap the stack results. 
+Check out [`Nep17TransferEvent`](https://github.com/CityOfZion/boa-test-constructor/blob/20a45755767b3d919bf7a594cfff6bff78cb72ac/boaconstructor/__init__.py#L302-L314)
+implementation for reference.
+
+```python
+    # inside the HelloWorldWithDeployTest class
+    async def test_gas_transfer_event(self):
+        # the amount of GAS tokens to transfer, since we will be invoking the transfer method, it's necessary to multiply by the decimals 
+        amount = 1 * 10**8
+        # calling the transfer method to emit a 'Transfer' event
+        result, notifications = await self.call(
+            "transfer", [self.user1.script_hash, self.genesis.script_hash, amount, None],
+            return_type=bool, target_contract=GAS, signing_accounts=[self.user1]
+        )
+        self.assertEqual(True, result)
+        self.assertEqual(1, len(notifications))
+        self.assertEqual("Transfer", notifications[0].event_name)
+
+        from boaconstructor import Nep17TransferEvent
+        # we can use the Nep17TransferEvent class to unwrap the stack items
+        transfer_event = Nep17TransferEvent.from_notification(notifications[0])
+        self.assertEqual(self.user1.script_hash, transfer_event.source)
+        self.assertEqual(self.genesis.script_hash, transfer_event.destination)
+        self.assertEqual(amount, transfer_event.amount)
+```