How to write unit test for Play Framework JSON readers - scala

Question

I wish to write unit test for the shipmentNumberValidator method, where Reads is play.api.libs.json.Reads. How do I do it?
object Validator {
def shipmentNumberValidator(): Reads[String] =
Reads.filter(ValidationError(ErrorConstants.BAD_SHIPMENT_NUMBER))(_.matches(BarcodePatterns.ShipmentNumber))
}
The unit test should pass it a shipment number, and the method returns either successfully the shipment number, or the error message if the shipment number format doesn't match. I don't know how to pass values to this method.
The method is usually used in companion objects for implicit reads, e.g.:
object ShipmentOrder {
implicit val shipmentOrderReads: Reads[ShipmentOrder] = (
(JsPath \ "id").read[String](Validator.missingFieldValidator("id") keepAnd Validator.shipmentNumberValidator())(ShipmentOrder.apply _)
}

Answer 1

Depending on the test framework you use (e.g. specs2), you can test expectations as following:
Doing a Json.parse("{expectedJson}") must be JsResult(expectedInstance)
Doing a Json.parse("{unexpectedJson}") must be JsError(_)
Using specs2:
import play.api.libs.json._
"JSON" should {
"be successfully parsed when expected" in {
Json.parse("""{"expected":"json"}""") must beLike[JsResult[ShipmentOrder]] {
case JsSuccess(parsed, _) =>
parsed must_== expectedShipmentOrder
}
}
"fail to be parsed if expected" in {
Json.parse("""{"unexpected":"json"}""") must beLike[JsResult[ShipmentOrder]] {
case JsError(details) =>
ok // possible check `details`
}
}
}