From 927c7c73b9766e825e1949667219ee367f342054 Mon Sep 17 00:00:00 2001
From: adamw <adam@warski.org>
Date: Mon, 13 Nov 2017 13:40:11 +0100
Subject: #43: supporting exceptions in the stub backend

---
 .../sttp/testing/SttpBackendStub.scala             | 12 +++++------
 .../sttp/testing/SttpBackendStubTests.scala        | 23 ++++++++++++++++++++++
 docs/backends/testing.rst                          | 12 +++++++++++
 3 files changed, 41 insertions(+), 6 deletions(-)

diff --git a/core/src/main/scala/com/softwaremill/sttp/testing/SttpBackendStub.scala b/core/src/main/scala/com/softwaremill/sttp/testing/SttpBackendStub.scala
index f62959f..b894e77 100644
--- a/core/src/main/scala/com/softwaremill/sttp/testing/SttpBackendStub.scala
+++ b/core/src/main/scala/com/softwaremill/sttp/testing/SttpBackendStub.scala
@@ -4,6 +4,7 @@ import com.softwaremill.sttp.testing.SttpBackendStub._
 import com.softwaremill.sttp.{MonadError, Request, Response, SttpBackend}
 
 import scala.language.higherKinds
+import scala.util.{Failure, Success, Try}
 
 /**
   * A stub backend to use in tests.
@@ -42,9 +43,10 @@ class SttpBackendStub[R[_], S] private (rm: MonadError[R],
     matchers
       .collectFirst {
         case matcher: Matcher[T @unchecked] if matcher(request) =>
-          matcher.response(request).get
+          Try(matcher.response(request).get)
       } match {
-      case Some(response) => wrapResponse(response)
+      case Some(Success(response)) => wrapResponse(response)
+      case Some(Failure(e))        => rm.error(e)
       case None =>
         fallback match {
           case None     => wrapResponse(DefaultResponse)
@@ -72,10 +74,9 @@ class SttpBackendStub[R[_], S] private (rm: MonadError[R],
       thenRespond(Response[Nothing](Left(msg), code, Nil, Nil))
     def thenRespond[T](body: T): SttpBackendStub[R, S] =
       thenRespond(Response[T](Right(body), 200, Nil, Nil))
-    def thenRespond[T](resp: Response[T]): SttpBackendStub[R, S] = {
+    def thenRespond[T](resp: => Response[T]): SttpBackendStub[R, S] = {
       val m = Matcher[T](p, resp)
       new SttpBackendStub(rm, matchers :+ m, fallback)
-
     }
   }
 }
@@ -124,8 +125,7 @@ object SttpBackendStub {
   }
 
   private object Matcher {
-
-    def apply[T](p: Request[T, _] => Boolean, response: Response[T]) = {
+    def apply[T](p: Request[T, _] => Boolean, response: => Response[T]) = {
       new Matcher[T]({
         case r if p(r) => response
       })
diff --git a/core/src/test/scala/com/softwaremill/sttp/testing/SttpBackendStubTests.scala b/core/src/test/scala/com/softwaremill/sttp/testing/SttpBackendStubTests.scala
index 9e10cd7..292d324 100644
--- a/core/src/test/scala/com/softwaremill/sttp/testing/SttpBackendStubTests.scala
+++ b/core/src/test/scala/com/softwaremill/sttp/testing/SttpBackendStubTests.scala
@@ -1,5 +1,9 @@
 package com.softwaremill.sttp.testing
 
+import java.util.concurrent.TimeoutException
+
+import scala.concurrent.ExecutionContext.Implicits.global
+
 import com.softwaremill.sttp._
 import org.scalatest.concurrent.ScalaFutures
 import org.scalatest.{FlatSpec, Matchers}
@@ -70,6 +74,25 @@ class SttpBackendStubTests extends FlatSpec with Matchers with ScalaFutures {
     ada.body should be(Right("Ada"))
   }
 
+  it should "handle exceptions thrown instead of a response (synchronous)" in {
+    implicit val s = SttpBackendStub(HttpURLConnectionBackend())
+      .whenRequestMatches(_ => true)
+      .thenRespond(throw new TimeoutException())
+
+    a[TimeoutException] should be thrownBy {
+      sttp.get(uri"http://example.org").send()
+    }
+  }
+
+  it should "handle exceptions thrown instead of a response (asynchronous)" in {
+    implicit val s = SttpBackendStub(new FutureMonad())
+      .whenRequestMatches(_ => true)
+      .thenRespond(throw new TimeoutException())
+
+    val result = sttp.get(uri"http://example.org").send()
+    result.failed.futureValue shouldBe a[TimeoutException]
+  }
+
   val testingStubWithFallback = SttpBackendStub
     .withFallback(testingStub)
     .whenRequestMatches(_.uri.path.startsWith(List("c")))
diff --git a/docs/backends/testing.rst b/docs/backends/testing.rst
index 1618d68..d1e99da 100644
--- a/docs/backends/testing.rst
+++ b/docs/backends/testing.rst
@@ -35,6 +35,18 @@ It is also possible to match request by partial function, returning a response.
 
 However, this approach has one caveat: the responses are not type-safe. That is, the backend cannot match on or verify that the type included in the response matches the response type requested.
 
+Simulating exceptions
+---------------------
+
+If you want to simulate an exception being thrown by a backend, e.g. a socket timeout exception, you can do so by throwing the appropriate exception instead of the response, e.g.::
+
+  implicit val testingBackend = SttpBackendStub(HttpURLConnectionBackend())
+    .whenRequestMatches(_ => true)
+    .thenRespond(throw new TimeoutException())
+
+Delegating to another backend
+-----------------------------
+
 It is also possible to create a stub backend which delegates calls to another (possibly "real") backend if none of the specified predicates match a request. This can be useful during development, to partially stub a yet incomplete API with which we integrate::
 
   implicit val testingBackend =
-- 
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