How Contracts Are Collected

When you call snforge test, one of the things that snforge does is that it calls Scarb, particularly scarb build. It makes Scarb build all contracts from your package and save them to the target/{current_profile} directory (read more on Scarb website).

Then, snforge loads compiled contracts from the package your tests are in, allowing you to declare the contracts in tests.

⚠️ Warning

Make sure to define [[target.starknet-contract]] section in your Scarb.toml, otherwise Scarb won't build your contracts.

Using External Contracts In Tests

If you wish to use contracts from your dependencies inside your tests (e.g. an ERC20 token, an account contract), you must first make Scarb build them. You can do that by using build-external-contracts property in Scarb.toml, e.g.: 

[[target.starknet-contract]]
build-external-contracts = ["openzeppelin::account::account::Account"]

For more information about build-external-contracts, see Scarb documentation.