Testing

Redstart has a built-in test runner that executes natively — no WASM, no Docker, no Matchstick. Tests live alongside your code in any .red module and run with redstart test.

test "a transfer debits the sender and credits the receiver" {
  Token.Transfer({ from: 0x01, to: 0x02, value: 100 })
  assertEq(Account.at(0x02).balance, 100)
  assert(Account.at(0x01).balance < 0)
}

A test fires events at your handlers against a mock store, then asserts on the resulting entity state.

Mocking contract calls

When a handler reads on-chain state, mock the call so the test stays deterministic:

test "approval writes the on-chain balance read via a contract call" {
  mockCall(ERC20.balanceOf(0x05), 4200)
  Token.Approval({ owner: 0x05, spender: 0x06, value: 1 })
  assertEq(Account.at(0x05).balance, 4200)
}

Running

redstart test              # run every test in the project
redstart test examples/erc20

Because the runner is native, the inner loop is near-instant — pair it with redstart dev to re-run check → build → test on every save.

Machine-readable diagnostics

For editors and AI-agent loops, redstart check --json emits diagnostics as JSON instead of prose:

redstart check --json

{
  "ok": false,
  "diagnostics": [
    {
      "severity": "error",
      "code": "E062",
      "message": "…",
      "help": "…",
      "file": "src/main.red",
      "line": 12,
      "column": 5,
      "offset": 240,
      "length": 7
    }
  ]
}

The process exits non-zero when ok is false, so an agent can read the error, apply the fix from help, and re-run — without parsing terminal output.