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§Testing your application with specs2

Writing tests for your application can be an involved process. Play provides a default test framework for you, and provides helpers and application stubs to make testing your application as easy as possible.

§Overview

The location for tests is in the “test” folder. There are two sample test files created in the test folder which can be used as templates.

You can run tests from the Play console.

Testing in Play is based on SBT, and a full description is available in the testing SBT chapter.

§Using specs2

In specs2, tests are organized into specifications, which contain examples which run the system under test through various different code paths.

Specifications extend the Specification trait and are using the should/in format:

import org.specs2.mutable._

class HelloWorldSpec extends Specification {

  "The 'Hello world' string" should {
    "contain 11 characters" in {
      "Hello world" must have size(11)
    }
    "start with 'Hello'" in {
      "Hello world" must startWith("Hello")
    }
    "end with 'world'" in {
      "Hello world" must endWith("world")
    }
  }
}

Specifications can be run in either IntelliJ IDEA (using the Scala plugin) or in Eclipse (using the Scala IDE). Please see the IDE page for more details.

NOTE: Due to a bug in the presentation compiler, tests must be defined in a specific format to work with Eclipse:

Here is a valid specification for Eclipse:

package models // this file must be in a directory called "models"

import org.specs2.mutable._
import org.specs2.runner._
import org.junit.runner._

@RunWith(classOf[JUnitRunner])
class ApplicationSpec extends Specification {
  ...
}

§Matchers

When you use an example, you must return an example result. Usually, you will see a statement containing a must:

"Hello world" must endWith("world")

The expression that follows the must keyword are known as matchers. Matchers return an example result, typically Success or Failure. The example will not compile if it does not return a result.

The most useful matchers are the match results. These are used to check for equality, determine the result of Option and Either, and even check if exceptions are thrown.

There are also optional matchers that allow for XML and JSON matching in tests.

§Mockito

Mocks are used to isolate unit tests against external dependencies. For example, if your class depends on an external DataService class, you can feed appropriate data to your class without instantiating a DataService object.

Mockito is integrated into specs2 as the default mocking library.

To use Mockito, add the following:

import org.specs2.mock._

and then add the library dependency to the build.

Using Mockito, you can mock out references to classes like so:

"MyService#isDailyData" should {
  "return true if the data is from today" in {
    val mockDataService = mock[DataService]
    mockDataService.findData returns Data(retrievalDate = new java.util.Date())

    val myService = new MyService() {
      override def dataService = mockDataService
    }

    val actual = myService.isDailyData
    actual must equalTo(true)
  }
}

Mocking is especially useful for testing the public methods of classes. Mocking objects and private methods is possible, but considerably harder.

§Unit Testing Models

Play does not require models to use a particular database data access layer. However, if the application uses Anorm or Slick, then frequently the Model will have a reference to database access internally.

import anorm._
import anorm.SqlParser._

case class User(id: String, name: String, email: String) {
   def roles = DB.withConnection { implicit connection =>
      ...
    }
}

For unit testing, this approach can make mocking out the roles method tricky.

A common approach is to keep the models isolated from the database and as much logic as possible, and abstract database access behind a repository layer.

case class Role(name:String)

case class User(id: String, name: String, email:String)
trait UserRepository {
  def roles(user:User) : Set[Role]
}
class AnormUserRepository extends UserRepository {
  import anorm._
  import anorm.SqlParser._

  def roles(user:User) : Set[Role] = {
    ...
  }
}

and then access them through services:

class UserService(userRepository : UserRepository) {

  def isAdmin(user:User) : Boolean = {
    userRepository.roles(user).contains(Role("ADMIN"))
  }
}

In this way, the isAdmin method can be tested by mocking out the UserRepository reference and passing it into the service:

object UserServiceSpec extends Specification with Mockito {

  "UserService#isAdmin" should {
    "be true when the role is admin" in {
      val userRepository = mock[UserRepository]
      userRepository.roles(any[User]) returns Set(Role("ADMIN"))

      val userService = new UserService(userRepository)
      val actual = userService.isAdmin(User("11", "Steve", "[email protected]"))
      actual must beTrue
    }
  }
}

§Unit Testing Controllers

Controllers are defined as objects in Play, and so can be trickier to unit test. In Play this can be alleviated by dependency injection using getControllerInstance. Another way to finesse unit testing with a controller is to use a trait with an explicitly typed self reference to the controller:

trait ExampleController {
  this: Controller =>

  def index() = Action {
    Ok("ok")
  }
}

object ExampleController extends Controller with ExampleController

and then test the trait:

object ExampleControllerSpec extends PlaySpecification with Results {

  class TestController() extends Controller with ExampleController

  "Example Page#index" should {
    "should be valid" in {
      val controller = new TestController()
      val result: Future[SimpleResult] = controller.index().apply(FakeRequest())
      val bodyText: String = contentAsString(result)
      bodyText must be equalTo "ok"
    }
  }
}

Next: Writing functional tests with specs2