Scala: 例外が発生するシナリオをテストする

例外が発生するのをテストにするには intercept を使う。

ExampleTestSuite.scala

import org.scalatest._

class ExampleTestSuite extends FunSuite with Matchers {

  test("invalid status transition") {
    val s = "hi"

    intercept[IndexOutOfBoundsException] {
		s.charAt(-1)
    }
  }
}

BDDらしく書く場合は、should be thrownBy、 thrownBy、 noException should be thrownBy などが使える

ExampleSpec.scala

import org.scalatest._

class ExampleSpec extends FeatureSpec with Matchers {
  scenario("Throws exception") {
    an[IndexOutOfBoundsException] should be thrownBy "".charAt(-1)
  }

  scenario("Throws exception with message") {
    val thrown = the[IndexOutOfBoundsException] thrownBy "".charAt(-1)
    thrown.getMessage shouldBe "String index out of range: -1"
  }

  scenario("Throws no exception") {
    noException should be thrownBy "a".charAt(0)
  }
}