add test to demonstrate hang

When using CatsResource with Specs2, if the resource acquisition raises
an exception, the tests will never start and the exception will never
be reported.

specs2/shared/src/test/scala/cats/effect/testing/specs2/CatsResourceErrorSpecs.scala

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2020 Typelevel
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package cats.effect.testing.specs2
+
+import cats.effect.{IO, Resource}
+import org.specs2.mutable.SpecificationLike
+import org.specs2.specification.core._
+
+import scala.concurrent.ExecutionContext.Implicits.global
+
+case class BlowUpResourceException() extends RuntimeException("boom")
+
+class CatsResourceErrorSpecs extends CatsResource[IO, Unit] with SpecificationLike {
+  val resource: Resource[IO, Unit] =
+    Resource.eval(IO.raiseError(BlowUpResourceException()))
+
+  var capture: Throwable = _
+
+  override def map(fs: =>Fragments): Fragments = {
+    super.map(fs)
+      .map {
+        case f@Fragment(_, e@Execution(Some(exec), _, _, _, _, _, _, _, _), _) =>
+          val newExec = (env: Env) =>
+            exec(env).recover {
+              case ex: BlowUpResourceException =>
+                () => {
+                  capture = ex
+                  success("mapped fragment")
+                }
+            }
+
+          f.copy(execution = e.copy(run = Some(newExec)))
+        case other => other
+      }
+  }
+
+  "cats resource support" should {
+    "report failure when the resource acquisition fails" in withResource { _ =>
+      IO(capture must not(beNull))
+    }
+  }
+}