FunctionBuilder mvp for a given/when/then test setup

_Usage.swift

test {
    "Hello world"

    given { print("GIVEN:", $0) }
    when { print("WHEN:", $0) }
    then { print("Then:", $0) }
}

GivenWhenThen.swift

import XCTest

@_functionBuilder
struct Test<T> {
    var data: T
    var given: given<T>
    var when: when<T>
    var then: then<T>

    func execute() {
        given.execute(data)
        when.execute(data)
        then.execute(data)
    }

    static func buildBlock(_ data: T, _ given: given<T>, _ when: when<T>, _ then: then<T>) -> Test {
        return Test(data: data, given: given, when: when, then: then)
    }
}
struct given<T> {
    let execute: (T) -> Void
}
struct when<T> {
    let execute: (T) -> Void
}
struct then<T> {
    let execute: (T) -> Void
}

func test<T>(@Test<T> test: () -> Test<T>) {
    test().execute()
}