SI-8475 Fix off by one in GroupedIterator when Streaming

This also affected sliding and grouped since they defer to GroupedIterator

1 files changed, 20 insertions, 0 deletions

diff --git a/test/junit/scala/collection/IteratorTest.scala b/test/junit/scala/collection/IteratorTest.scala
new file mode 100644
index 0000000000..cb7cbb40bc
--- /dev/null
+++ b/test/junit/scala/collection/IteratorTest.scala
@@ -0,0 +1,20 @@
+
+package scala.collection
+
+import org.junit.Assert._
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.junit.runners.JUnit4
+
+@RunWith(classOf[JUnit4])
+class IteratorTest {
+
+  @Test
+  def groupedIteratorShouldNotAskForUnneededElement(): Unit = {
+    var counter = 0
+    val it = new Iterator[Int] { var i = 0 ; def hasNext = { counter = i; true } ; def next = { i += 1; i } }
+    val slidingIt = it sliding 2
+    slidingIt.next
+    assertEquals("Counter should be one, that means we didn't look further than needed", 1, counter)
+  }
+}