ScalaCheck中forAll代码体未执行问题求助

我编写了一段测试ResizableRectangle表面积的Scala代码，通过ScalaCheck生成随机整数作为矩形的坐标和尺寸参数。运行测试后仅打印出"begin"，从未打印"inner body"，但我预期会多次输出该内容。请问我哪里出错或遗漏了？

原代码如下：

package de.thm.move.shapes
import de.thm.move.views.shapes.ResizableRectangle
import org.scalacheck.*
import de.thm.move.MoveSpec

class ResizableRectangleTest extends MoveSpec {

  "Rectangle area procedure" should "give the correct area" in{
    val intPositiveDomain = Gen.choose[Int](1, 10000) //for the coordinates of the shape
    val intDomain = Gen.choose[Int](-10000, 10000) //for the size of the shape

    println("begin")
    //will test for random values for the coordinates and the size of the shape
    val popRectangle =  Prop.forAll(intDomain,intDomain,intPositiveDomain,intPositiveDomain) { (x: Int, y: Int, width: Int, height: Int) =>
      val rectangle: ResizableRectangle = new ResizableRectangle((x.toDouble, y.toDouble), width.toDouble, height.toDouble)
      val correctSurface: Double = width.toDouble * height.toDouble
      println("inner body")
      rectangle.getSurfaceArea() == correctSurface
    }

  }
}

问题原因与修复方案 #

你只定义了ScalaCheck的Prop属性实例，但没有触发测试执行。Prop.forAll只是创建了一个待测试的属性对象，不会自动运行测试用例，必须显式执行才能让ScalaCheck生成随机参数并运行内部代码。

方案1：手动调用check()方法 #

直接在属性定义后调用check()方法，触发测试执行：

package de.thm.move.shapes
import de.thm.move.views.shapes.ResizableRectangle
import org.scalacheck.*
import de.thm.move.MoveSpec

class ResizableRectangleTest extends MoveSpec {

  "Rectangle area procedure" should "give the correct area" in{
    val intPositiveDomain = Gen.choose[Int](1, 10000) //坐标参数
    val intDomain = Gen.choose[Int](-10000, 10000) //尺寸参数

    println("begin")
    val popRectangle =  Prop.forAll(intDomain,intDomain,intPositiveDomain,intPositiveDomain) { (x: Int, y: Int, width: Int, height: Int) =>
      val rectangle: ResizableRectangle = new ResizableRectangle((x.toDouble, y.toDouble), width.toDouble, height.toDouble)
      val correctSurface: Double = width.toDouble * height.toDouble
      println("inner body")
      rectangle.getSurfaceArea() == correctSurface
    }
    // 触发测试执行
    popRectangle.check()
  }
}

方案2：使用ScalaTest集成的ScalaCheck支持（推荐） #

由于你的测试类继承了MoveSpec（基于ScalaTest），更规范的做法是导入ScalaTest与ScalaCheck的集成特质，直接用集成的forAll自动执行测试：

package de.thm.move.shapes
import de.thm.move.views.shapes.ResizableRectangle
import org.scalacheck.Gen
import org.scalatestplus.scalacheck.ScalaCheckPropertyChecks
import de.thm.move.MoveSpec

class ResizableRectangleTest extends MoveSpec with ScalaCheckPropertyChecks {

  "Rectangle area procedure" should "give the correct area" in {
    val intPositiveDomain = Gen.choose[Int](1, 10000) //坐标参数
    val intDomain = Gen.choose[Int](-10000, 10000) //尺寸参数

    println("begin")
    // 集成式forAll会自动执行测试，无需手动调用check
    forAll(intDomain, intDomain, intPositiveDomain, intPositiveDomain) { (x: Int, y: Int, width: Int, height: Int) =>
      val rectangle: ResizableRectangle = new ResizableRectangle((x.toDouble, y.toDouble), width.toDouble, height.toDouble)
      val correctSurface: Double = width.toDouble * height.toDouble
      println("inner body")
      rectangle.getSurfaceArea() == correctSurface
    }
  }
}

两种方案都能让ScalaCheck生成随机参数并执行内部代码，你会看到多次输出"inner body"。

内容的提问来源于stack exchange，提问作者Daaninator