## Testing a Vyper Contract with Mocks In this lesson, we'll be working on a Vyper contract. To test this contract, we use Mocks, a Python library that lets us create and interact with dummy objects, allowing us to isolate and test specific parts of our code. We'll create tests using the Arrange, Act, Assert (AAA) framework. This approach helps structure our tests for readability and clarity. **Arrange** involves setting up everything necessary for the test. For example, we'll deploy a mock version of our contract. **Act** will be the action we are testing - for example, calling a specific function in our contract. **Assert** will be the final step where we make sure that the action performed in the Act section delivers the expected outcome. The following is an example of the code we will be working with: ```python def test_can_change_values(): # Arrange favorites_contract = deploy_favorites() # Act favorites_contract.store(42) # Assert assert favorites_contract.retrieve() == 42 ``` We are testing a function called 'store' in this example. First, we **arrange** by deploying our contract using 'deploy_favorites()'. Then, we **act** by calling 'store(42)' on our contract. Finally, we **assert** that 'retrieve()' on our contract returns the expected value (42). We'll now add another test, this time we'll make sure we can add people to our contract. We can use the existing contract structure, but this time we'll need to test the 'add_person' functionality: ```python def test_can_add_people(): # Arrange new_person = "Becca" favorite_number = 16 favorites_contract = deploy_favorites() # Act favorites_contract.add_person(new_person, favorite_number) # Assert assert favorites_contract.list_of_people(0) == (favorite_number, new_person) ``` Let's run the tests we've created. ```bash mox test ``` This command will run all of our tests, and it will output the results. We can also run just one test using the **-k** flag: ```bash mox test -k test_can_add_people ``` This command will run only the 'test_can_add_people' test, making it easier to troubleshoot individual tests if needed.