Merge pull request #726 from ceedubs/moar-streamingt-tests

Add some StreamingT tests

core/src/main/scala/cats/data/StreamingT.scala

@@ -351,7 +351,9 @@ object StreamingT extends StreamingTInstances {
     Cons(a, fs)
 
   /**
-   * Create a stream from an `F[StreamingT[F, A]]` value.
+   * Create a stream from a deferred `StreamingT[F, A]` value.
+   * Note: the extent to which this defers the value depends on the `pureEval`
+   * implementation of the `Applicative[F]` instance.
    */
   def defer[F[_], A](s: => StreamingT[F, A])(implicit ev: Applicative[F]): StreamingT[F, A] =
     Wait(ev.pureEval(Always(s)))

tests/src/test/scala/cats/tests/StreamingTTests.scala

@@ -3,7 +3,7 @@ package tests
 
 import algebra.laws.OrderLaws
 
-import cats.data.StreamingT
+import cats.data.{Streaming, StreamingT}
 import cats.laws.discipline.{CoflatMapTests, MonadCombineTests, SerializableTests}
 import cats.laws.discipline.arbitrary._
 import cats.laws.discipline.eq._
@@ -147,6 +147,29 @@ class StreamingTTests extends CatsSuite {
     }
   }
 
+  test("unfold with Id consistent with Streaming.unfold") {
+    forAll { (o: Option[Long]) =>
+      val f: Long => Option[Long] = { x  =>
+        val rng = new scala.util.Random(x)
+        if (rng.nextBoolean) Some(rng.nextLong)
+        else None
+      }
+
+      StreamingT.unfold[Id, Long](o)(f).toList should === (Streaming.unfold(o)(f).toList)
+    }
+  }
+
+  test("defer produces the same values") {
+    forAll { (xs: StreamingT[Option, Int]) =>
+      StreamingT.defer(xs) should === (xs)
+    }
+  }
+
+  test("defer isn't eager if the pureEval impl isn't") {
+    def s: StreamingT[Eval, Int] = throw new RuntimeException("blargh")
+    val x = StreamingT.defer[Eval, Int](s)
+  }
+
   test("fromVector") {
     forAll { (xs: Vector[Int]) =>
       StreamingT.fromVector[Id, Int](xs).toList.toVector should === (xs)