SixSidedDie.swift

import Foundation

actor SixSidedDie {

	struct Environment: Sendable {

		var doTheThing: @Sendable (_ range: ClosedRange<Int>) -> Int

	}

	private var environment = Environment(
		doTheThing: { Int.random(in: $0) }
	)

	func updateEnvironment<T>(_ handler: (_ environment: inout Environment) -> T) -> T {
		handler(&environment)
	}

	func roll() -> Int {
		environment.doTheThing(1...6)
	}

}

class SixSidedDieTests {

	func testRanges() async {
		let die = SixSidedDie()

		let ranges = await die.updateEnvironment { environment in
			return AsyncStream { continuation in
				environment.doTheThing = { [original = environment.doTheThing] range in
					continuation.yield(range)
					return original(range)
				}
			}
		}

		await die.roll()
		await die.roll()
		await die.roll()

		await print(ranges.allSatisfy { $0 == 1...6 })
	}

}

Task {
	await SixSidedDieTests().testRanges()
}