## Testing We've built out our stablecoin engine. Now, the next step is to make sure it works correctly by adding tests. First, we'll set up a conftest.py file to help us with our testing. We'll add a few session-scoped fixtures to help us quickly grab the information we need. ```python from moccasin.config import get_active_network import pytest @pytest.fixture(scope="session") def active_network(): return get_active_network() @pytest.fixture(scope="session") def weth(active_network): return active_network.manifest_named("weth") @pytest.fixture(scope="session") def wbtc(active_network): return active_network.manifest_named("wbtc") @pytest.fixture(scope="session") def eth_usdc(active_network): return active_network.manifest_named("eth_usd_price_feed") @pytest.fixture(scope="session") def btc_usd(active_network): return active_network.manifest_named("btc_usd_price_feed") ``` Next, we'll create a fixture for our decentralized stablecoin engine. ```python @pytest.fixture def dsc(active_network): return active_network.manifest_named("dsc") @pytest.fixture def dsce(active_network): return active_network.manifest_named("dsce") ``` We also need a fixture to create a user with a starting balance of 10 ETH. ```python from eth.account import Account import boa from eth.utils import to_wei BALANCE = to_wei(10, "ether") @pytest.fixture def some_user(weth, wbtc): entropy = 13 account = Account.create(entropy) boa.env.set_balance(account.address, BALANCE) with boa.env.prank(account.address): weth.mock_mint(BALANCE) wbtc.mock_mint(1) return account.address ``` Now we're ready to write some tests. We'll create a tests/unit/tests*dsc_engine.py file and write some tests for the \_init* method of the decentralized stablecoin engine. ```python from src import dsc_engine import pytest from eth_codex.abi.exceptions import EncodeError from tests.conftest import COLLATERAL_AMOUNT def test_reverts_if_token_lengths_are_different(dsc, eth_usd, btc_usd, weth, wbtc): with pytest.raises(EncodeError): dsc_engine.deploy(wbtc, weth, weth, eth_usd, btc_usd, dsc.address) def test_reverts_if_collateral_zero(some_user, weth, dsce): with boa.env.prank(some_user): weth.approve(dsce, COLLATERAL_AMOUNT) dsce.deposit_collateral(weth, 0) ``` We'll use the pytest.raises() context manager to test that the code raises an EncodeError when it is passed an invalid set of token addresses. We also test that the deposit_collateral() method reverts when passed a collateral amount of 0. Now, let's run our tests. ```bash mox test ``` If we run this command, we'll see all of our tests pass. We'll soon get to the workshop, where you'll write more tests to ensure our code works as expected.