## Branching Tree Technique

The [Branching Tree Technique (BTT)](https://github.com/PaulRBerg/btt-examples) is a methodology for organizing Solidity tests by modeling all conditions and outcomes as a decision tree. Branches represent conditions and leaves represent concrete test cases.

BTT fits Foundry tests because each leaf can become a `test` or `test_RevertWhen` function, while each condition can become setup code or a modifier. For example, a `TransferTest` tree can describe the paused and balance states for a transfer:

```txt
TransferTest
├── When paused
│   └── It should revert.
└── When not paused
    ├── When balance is insufficient
    │   └── It should revert.
    └── When balance is sufficient
        └── It should transfer the tokens.
```

That tree can be implemented manually in a Foundry test file:

```solidity
contract TransferTest is Test {
    modifier whenNotPaused() {
        _;
    }

    modifier whenBalanceIsSufficient() {
        _;
    }

    function test_ShouldTransferTheTokens()
        public
        whenNotPaused
        whenBalanceIsSufficient
    {
        // arrange, act, assert
    }

    function test_RevertWhen_Paused() public {
        // arrange, act, assert
    }
}
```

### Bulloak

[Bulloak](https://bulloak.dev/) is a CLI tool that automates BTT workflows with Foundry. It takes a `.tree` spec file as input and can:

* **Scaffold** a Solidity test file from the tree
* **Check** that an existing test file matches the tree spec

**Install:**

```bash
cargo install bulloak
```

**Create a spec file (`TransferTest.tree`):**

```txt
TransferTest
└── When not paused
    ├── When balance is insufficient
    │   └── It should revert.
    └── When balance is sufficient
        └── It should transfer the tokens.
```

**Scaffold a test file:**

```bash
bulloak scaffold TransferTest.tree
```

**Check an existing test file matches the spec:**

```bash
bulloak check TransferTest.tree
```

Bulloak generates standard Solidity test skeletons that you fill in with setup and assertions, then run with `forge test`.

For more information see the [Bulloak GitHub](https://github.com/alexfertel/bulloak) and the [BTT presentation at Solidity Summit 2023](https://prberg.com/presentations/solidity-summit-2023/).