Using JUnit @Rule with ScalaTest (e.g. TemporaryFolder)

问题

I would like to be able to use JUnit rules such as TemporaryFolder or other TestRules we have already developed in-house. What is the best method to accomplish that? I'm aware of JUnitSuite but it doesn't seem to pick up the @Rule annotation. I would like to use a different ScalaTest suite anyway.

So my questions are:

Are JUnit rules supported by a ScalaTest suit?
If not, is there a library out there which would make using Junit TestRules possible?
If not, how to use JUnit TestRules in Scala tests?
Or is there a more appropriate Scala-specific approach for acomplishing what TemporaryFolder, or, e.g., Stefan Birkner's System Rules provide?

Here's what I tried with JUnitSuite:

class MyTest extends JUnitSuite {
  //@Rule
  //val temporaryFolder = new TemporaryFolder() // throws java.lang.Exception: The @Rule 'temporaryFolder' must be public.

  @Rule
  def temporaryFolder = new TemporaryFolder()

  @Test
  def test: Unit = {
    assert(temporaryFolder.newFile() !== null) // java.lang.IllegalStateException: the temporary folder has not yet been created
  }
}

回答1:

You could solve the problem by creating a member field of type TemporaryFolder and returning this field value by the @Rule function.

class MyTest extends JUnitSuite {

  val _temporaryFolder = new TemporaryFolder

  @Rule
  def temporaryFolder = _temporaryFolder

  @Test
  def test: Unit = {
    assert(temporaryFolder.newFile() !== null)
  }
}

回答2:

Here is what I came up based on ScalaTest's documentation on fixtures. Still, I would like to know if there is a better solution.

Loan-fixture method

class LoanFixtureTest extends FunSuite {
  def withRule[T <: TestRule](rule: T)(testCode: T => Any): Unit = {
    rule(
      new Statement() {
        override def evaluate(): Unit = testCode(rule)
      },
      Description.createSuiteDescription("JUnit rule wrapper")
    ).evaluate()
  }

  test("my test") {
    withRule(new TemporaryFolder()) { temporaryFolder =>
      assert(temporaryFolder.newFile() !== null)
    }
  }
}

Pros: allows applying the rule only to tests where it is needed
Cons: not very elegant usage; clumsy when multiple TestRules are required

Using stackable mixins with withFixture(test: NoArgTest) override

trait TemporaryFolderFixture1 extends SuiteMixin {
  this: Suite =>
  val temporaryFolder = new TemporaryFolder

  abstract override def withFixture(test: NoArgTest) = {
    var outcome: Outcome = null
    val statementBody = () => outcome = super.withFixture(test)
    temporaryFolder(
      new Statement() {
        override def evaluate(): Unit = statementBody()
      },
      Description.createSuiteDescription("JUnit rule wrapper")
    ).evaluate()
    outcome
  }
}

class StackableTraitFixtureTest extends FunSuite with TemporaryFolderFixture1 {
  test("my test") {
    assert(temporaryFolder.newFile() !== null)
  }
}

Pros: very simple usage, conveniently allows mixing multiple rules in
Cons: requires having a mixin for every rule; rules need to be invoked even for tests that don't need them; rule cannot be used e.g. in BeforeAfterEach#beforeEach()

Overriding withFixture(test: OneArgTest)

trait TemporaryFolderFixture2 {
  thisFixture: org.scalatest.fixture.FunSuite =>
  type FixtureParam = TemporaryFolder

  override protected def withFixture(test: OneArgTest): Outcome = {
    val temporaryFolder = new TemporaryFolder()
    var outcome: Outcome = null
    temporaryFolder(
      new Statement() {
        override def evaluate(): Unit = {
          outcome = withFixture(test.toNoArgTest(temporaryFolder))
        }
      },
      Description.createSuiteDescription("JUnit rule wrapper")
    ).evaluate()
    outcome
  }
}

class OneArgWithFixtureTest extends org.scalatest.fixture.FunSuite with TemporaryFolderFixture2 {
  test("my test") { temporaryFolder =>
    assert(temporaryFolder.newFile() !== null)
  }
}

Cons: allows only one TestRule, making in generic to work with any rule instead of just TestRule would require an extra effort

Which one do you like the best?

回答3:

This worked for me. Based on answer. So annotation will be applied to to the (synthetic) getter method

import org.junit._
import scala.annotation.meta.getter

class MyTest extends JUnitSuite {

  @(Rule @getter)
  val tempFolder = new TemporaryFolder

}

Just make sure to use junit version >4.11.

来源：https://stackoverflow.com/questions/32160549/using-junit-rule-with-scalatest-e-g-temporaryfolder

标签

scala

unit-testing

junit

scalatest