How can I test scala.js programs for side effects that happen asynchronously using μtest?
I have a μtest package that is supposed to check that some asynchronous operation eventually has a side effect. Since javascript (and thus scala.js) is single threaded, it is not possible to block and wait for a side effect. Also, the μtest method does eventually
not work in the javascript runtime. How do you perform such a test?
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1 answer
If you return Future
from μtest, then the test will pass if the future succeeds and fail if the future fails. This way, you can schedule a conditional check at some point in the future without blocking.
I wrote a simple method eventually
that accomplishes this:
package utest
import rx.ops.DomScheduler
import scala.concurrent.{Promise, Future}
import scala.concurrent.duration.FiniteDuration
import scala.util.{Failure, Success, Try}
object JsOps {
import scala.concurrent.ExecutionContext.Implicits.global
val scheduler = new DomScheduler
def eventually(eval: => Try[Boolean])(implicit timeout: FiniteDuration): Future[Boolean] = {
val p = Promise[Boolean]()
scheduler.scheduleOnce(timeout) {
eval match {
case Success(b) => p.success(b)
case Failure(t) => p.failure(t)
}
}
p.future
}
}
Here's a usage example:
import scala.concurrent.duration._
implicit val timeout = 30.milliseconds
eventually {
if (/*condition holds true*/) {
Success(true)
} else Failure(new RuntimeException(/*error message*/))
}
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