Write tests, mock collaborators, and pin a `Mock[T]`

Goal: write and run tests, assert outcomes, fabricate values, and replace a dependency.

Tests live in a project’s tests/ tree (see Lay out a project). A test file is a test block naming its target unit, containing named cases.

Write and run

test counters {
  test "a fresh counter starts at zero" {
    let n <- Counter(CounterId.unsafe("fresh")).current()
    assert n == 0
  }
}

Run the suite:

bynkc test .

bynkc test compiles the project, type-checks it with tsc, and runs it with Node, so both must be on your path. assert is valid only inside a test case.

Fabricate values with Mock[T]

Mock[T] produces a value of T. For a refined type it satisfies the refinement; pass an argument to pin a specific value:

test quantities {
  test "mocks" {
    let a = Mock[Quantity]       -- a valid Quantity
    let b = Mock[Quantity](50)   -- pinned to 50
    assert a == a
    assert b == b
  }
}

A Matches-refined string cannot be fabricated blindly — a bare Mock of one is rejected (bynk.mock.needs_pin); pin it instead. Mock[T] is test-only.

Mock a collaborator with mocks

Replace a capability the code under test depends on:

test payments {
  mocks Logger = SilentLogger {
    fn log(msg: String) -> Effect[()] {
      ()
    }
  }

  test "authorise succeeds for a positive amount" {
    let r <- authorise.call(100)
    assert r is Ok(_)
  }
}

The SilentLogger stands in for the real Logger for these cases.

Related

• Tutorial: Test it.
• Reference: testing.
• Troubleshooting: bynk.mock.* errors.