Testing Scala Futures with ScalaTest 2.0

Recently I was writing integration tests for a library that returned futures. I wanted simple synchronous tests.

Fortunately in the latest release of ScalaTest they have added something to do just that: the ScalaFutures trait

Say you have a class that returns a Future, e.g:

	class ClassThatReturnsFutures() {
	def goDoSomething() : Future[String] = {
	future {
	println("I best do this asynchronously")
	"The result"
	}
	}
	}

view raw ClassThatReturnsFutures.scala hosted with ❤ by GitHub

And you want to write a test for this and you want to wait for the future to complete. In regular code you might use a call back or a for comprehension e.g:

	test("Test a asynchronous method synchronously") {
	val underTest = new ClassThatReturnsFutures()
	val futureResult = underTest.goDoSomething()
	futureResult onComplete {
	case Success(value) => value should equal("Something")
	case Failure(exp) => fail(exp)
	}
	}

view raw ClassThatReturnsFuturesTest.scala hosted with ❤ by GitHub

This won't work in a test as the test will finish before the future completes and the assertions are on a different thread.

ScalaFutures to the rescue! Upgrade to ScalaTest 2.0+ and mix in the ScalaFutures trait. Now you can test using whenReady:

	test("Test a asynchronous method synchronously - whenReady") {
	val underTest = new ClassThatReturnsFutures()
	val futureResult = underTest.goDoSomething()
	whenReady(futureResult) { result =>
	result should equal("The result")
	}
	}

view raw ClassThatReturnsFuturesTest.scala hosted with ❤ by GitHub

Or with futureValue:

	test("Test a asynchronous method synchronously - futureResult") {
	val underTest = new ClassThatReturnsFutures()
	val futureResult = underTest.goDoSomething()
	futureResult.futureValue should equal("The result")
	}

view raw ClassThatReturnsFuturesTest.scala hosted with ❤ by GitHub

Happy testing! Full source code here.