Scalatest sharing service instance across multiple test suites - dependency-injection

Question

I have FlatSpec test classes which need to make use of a REST service for some fixture data. When running all the tests in one go I only really want to instantiate the REST client once as it may be quite expensive. How can I go about this and can I also get it to work for running just one test class when I am running in my IDE?

Answer 1

1. Use mocking:
I would advice you to use some kind of mocking when you try to test REST service. You can try for example scala-mock. Creation of mock service isn't time/cpu consuming, so you can create mocks in all your tests and don't need to share them.
Look:
trait MyRestService {
def get(): String
}
class MyOtherService(val myRestService: MyRestService) {
def addParentheses = s"""(${myRestService.getClass()})"""
}
import org.scalamock.scalatest.MockFactory
class MySpec extends FreeSpec with MockFactory {
"test1 " in {
// create mock rest service and define it's behaviour
val myRestService = mock[MyRestService]
val myOtherService = new MyOtherService(myRestService)
inAnyOrder {
(myRestService.get _).expects().returning("ABC")
}
//now it's ready, you can use it
assert(myOtherService.addParentheses === "(ABC)")
}
}
2. Or use Sharing fixtures:
If you still want to use real implementation of you REST service and create only one instance and then share it with some test condider using:
get-fixture methods => Use it when you need the same mutable fixture objects in multiple tests, and don't need to clean up after.
withFixture(OneArgTest) => Use when all or most tests need the same fixtures that must be cleaned up afterwords.
Refer to http://www.scalatest.org/user_guide/sharing_fixtures#loanFixtureMethods for more details and code examples.
If you want to share the same fixture against multiple Suites use org.scalatest.Suites and #DoNotDiscover annotation (these requires at least scalatest-2.0.RC1)

Answer 2

Pawel's last comment fits well.
It was easier by inheriting from Suite with BeforaAndAfterAll instead of Suites.
import com.typesafe.config.ConfigFactory
import com.google.inject.Guice
import org.scalatest.{BeforeAndAfterAll, Suite}
import net.codingwell.scalaguice.InjectorExtensions.ScalaInjector
class EndToEndSuite extends Suite with BeforeAndAfterAll {
private val injector = {
val config = ConfigFactory.load
val module = new AppModule(config) // your module here
new ScalaInjector(Guice.createInjector(module))
}
override def afterAll {
// your shutdown if needed
}
override val nestedSuites = collection.immutable.IndexedSeq(
injector.instance[YourTest1],
injector.instance[YourTest2] //...
)
}