test demo.shapes {
  -- v0.9.4 Part B (slice 2): bare `Mock[T]` generation for sum, record, and
  -- opaque types.
  test "bare sum mock takes the first declared variant" {
    let s = Mock[Status]
    assert s is Active(_)
  }

  test "bare record mock fills every field, including an opaque one" {
    let c = Mock[Cart]
    assert c.count == c.count
  }
}
