Question

作为练习的一部分，我正在编写一个API来生成随机数。这是我的代码，我想测试notNegativeInt函数。

我该怎么做？

（这里是完整的解决方案https://github.com/fpinscala/fpinscala/blob/master/answers/src/main/scala/fpinscala/state/State.scala）

import java.util.Random

object chapter6 {
  println("Welcome to the Scala worksheet")       //> Welcome to the Scala worksheet

  trait RNG {
    def nextInt: (Int, RNG) // Should generate a random `Int`. We'll later define other functions in terms of `nextInt`.
  }

  object RNG {
    // NB - this was called SimpleRNG in the book text
    case class Simple(seed: Long) extends RNG {
      def nextInt: (Int, RNG) = {
        val newSeed = (seed * 0x5DEECE66DL + 0xBL) & 0xFFFFFFFFFFFFL // `&` is bitwise AND. We use the current seed to generate a new seed.
        val nextRNG = Simple(newSeed) // The next state, which is an `RNG` instance created from the new seed.
        val n = (newSeed >>> 16).toInt // `>>>` is right binary shift with zero fill. The value `n` is our new pseudo-random integer.
        (n, nextRNG) // The return value is a tuple containing both a pseudo-random integer and the next `RNG` state.
      }
    }
    // We need to be quite careful not to skew the generator.
    // Since `Int.Minvalue` is 1 smaller than `-(Int.MaxValue)`,
    // it suffices to increment the negative numbers by 1 and make them positive.
    // This maps Int.MinValue to Int.MaxValue and -1 to 0.
    def nonNegativeInt(rng: RNG): (Int, RNG) = {
      val (i, r) = rng.nextInt
      (if (i < 0) -(i + 1) else i, r)
    }



  }



}

Answer 1

如果只想测试nonNegativeInt方法，可以提供RNG的模拟实现，它提供了在调用nextInt时要测试的值。例如，nonNegativeInt中有2个可能的分支，因此您应该提供一个提供负数的RNG实例和另一个提供正数的实例。

class MyRNG(val num:Int) extends RNG {
  self: RNG => 
    def nextInt: (Int, RNG) = (num, this)
}

使用此RNG模拟，您可以测试您的nonNegativeInt方法，创建一个具有您想要测试的所需值的MyRNG。

对于这种特殊情况，您也可以省略自引用：

class MyRNG(val num:Int) extends RNG {
  def nextInt: (Int, RNG) = (num, this)
}

如何测试对象方法（练习）

1 个答案: