2 files changed, 24 insertions, 0 deletions
diff --git a/test/files/run/t6198.check b/test/files/run/t6198.check
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/test/files/run/t6198.check
diff --git a/test/files/run/t6198.scala b/test/files/run/t6198.scala
new file mode 100644
index 0000000000..5aa8f1c1cf
--- /dev/null
+++ b/test/files/run/t6198.scala
@@ -0,0 +1,24 @@
+import scala.collection.immutable._
+
+object Test extends App {
+  // test that ListSet.tail does not use a builder
+  // we can't test for O(1) behavior, so the best we can do is to
+  // check that ls.tail always returns the same instance
+  val ls = ListSet.empty[Int] + 1 + 2
+
+  if(ls.tail ne ls.tail)
+    println("ListSet.tail should not use a builder!")
+
+  // class that always causes hash collisions
+  case class Collision(value:Int) { override def hashCode = 0 }
+
+  // create a set that should have a collison
+  val x = HashSet.empty + Collision(0) + Collision(1)
+  if(x.getClass.getSimpleName != "HashSetCollision1")
+    println("HashSet of size >1 with collisions should use HashSetCollision")
+
+  // remove the collision again by removing all but one element
+  val y = x - Collision(0)
+  if(y.getClass.getSimpleName != "HashSet1")
+    println("HashSet of size 1 should use HashSet1" + y.getClass)
+}