Extent

Sealed supertrait for Length and Size type classes.

These traits enable you to use ScalaTest matchers' “have length” and “have size” syntax to be used with arbitrary objects. As an example, consider java.net.DatagramPacket, which has a getLength method. By default, this can't be used with ScalaTest's have length syntax.

scala> import java.net.DatagramPacket
import java.net.DatagramPacket

scala> import org.scalatest.matchers.ShouldMatchers._
import org.scalatest.matchers.ShouldMatchers._

scala> val dp = new DatagramPacket(Array(0x0, 0x1, 0x2, 0x3), 4)
dp: java.net.DatagramPacket = java.net.DatagramPacket@54906181

scala> dp.getLength
res0: Int = 4

scala> dp should have length 4
:13: error: could not find implicit value for parameter ev: org.scalatest.matchers.ShouldMatchers.Extent[java.net.DatagramPacket]
         dp should have length 4
            ^

scala> implicit val lengthOfDatagramPacket =
    |   new Length[DatagramPacket] {
    |     def extentOf(dp: DatagramPacket): Long = dp.getLength
    |   }
lengthOfDatagramPacket: java.lang.Object with org.scalatest.matchers.ShouldMatchers.Length[java.net.DatagramPacket] = $anon$1@550c6b37

scala> dp should have length 4

scala> dp should have length 3
org.scalatest.exceptions.TestFailedException:  java.net.DatagramPacket@54906181 had length 4, not length 3