Re-enable RedBlack's ScalaCheck test, which was disabled at r21829.

I haven't been able to find any reason for that reversal, but
this version is an improved version provided with SI-3796, which
never got committed along with the patch.

This version generates trees directly instead of using the methods
under test. It also puts an upper bound on tree size and, therefore,
execution time.

1 files changed, 213 insertions, 0 deletions

diff --git a/test/files/scalacheck/redblack.scala b/test/files/scalacheck/redblack.scala
new file mode 100644
index 0000000000..1fcaa46f0e
--- /dev/null
+++ b/test/files/scalacheck/redblack.scala
@@ -0,0 +1,213 @@
+import org.scalacheck._
+import Prop._
+import Gen._
+
+/*
+Properties of a Red & Black Tree:
+
+A node is either red or black.
+The root is black. (This rule is used in some definitions and not others. Since the
+root can always be changed from red to black but not necessarily vice-versa this 
+rule has little effect on analysis.)
+All leaves are black.
+Both children of every red node are black.
+Every simple path from a given node to any of its descendant leaves contains the same number of black nodes.
+*/
+
+abstract class RedBlackTest extends Properties("RedBlack") {
+  def minimumSize = 0
+  def maximumSize = 5
+
+  object RedBlackTest extends scala.collection.immutable.RedBlack[String] {
+    def isSmaller(x: String, y: String) = x < y
+  }
+  
+  import RedBlackTest._
+  
+  def nodeAt[A](tree: Tree[A], n: Int): Option[(String, A)] = if (n < tree.iterator.size && n >= 0)
+    Some(tree.iterator.drop(n).next)
+  else
+    None
+    
+  def treeContains[A](tree: Tree[A], key: String) = tree.iterator.map(_._1) contains key
+  
+  def mkTree(level: Int, parentIsBlack: Boolean = false, label: String = ""): Gen[Tree[Int]] = 
+    if (level == 0) {
+      value(Empty)
+    } else {
+      for {
+        oddOrEven <- choose(0, 2)
+        tryRed = oddOrEven.sample.get % 2 == 0 // work around arbitrary[Boolean] bug
+        isRed = parentIsBlack && tryRed
+        nextLevel = if (isRed) level else level - 1
+        left <- mkTree(nextLevel, !isRed, label + "L")
+        right <- mkTree(nextLevel, !isRed, label + "R")
+      } yield {
+        if (isRed) 
+          RedTree(label + "N", 0, left, right)
+        else
+          BlackTree(label + "N", 0, left, right)
+      }
+    }
+
+  def genTree = for {
+    depth <- choose(minimumSize, maximumSize + 1)
+    tree <- mkTree(depth)
+  } yield tree
+  
+  type ModifyParm
+  def genParm(tree: Tree[Int]): Gen[ModifyParm]
+  def modify(tree: Tree[Int], parm: ModifyParm): Tree[Int]
+  
+  def genInput: Gen[(Tree[Int], ModifyParm, Tree[Int])] = for {
+    tree <- genTree
+    parm <- genParm(tree)
+  } yield (tree, parm, modify(tree, parm))
+}
+
+trait RedBlackInvariants {
+  self: RedBlackTest =>
+  
+  import RedBlackTest._
+    
+  def rootIsBlack[A](t: Tree[A]) = t.isBlack
+  
+  def areAllLeavesBlack[A](t: Tree[A]): Boolean = t match {
+    case Empty => t.isBlack
+    case ne: NonEmpty[_] => List(ne.left, ne.right) forall areAllLeavesBlack
+  }
+  
+  def areRedNodeChildrenBlack[A](t: Tree[A]): Boolean = t match {
+    case RedTree(_, _, left, right) => List(left, right) forall (t => t.isBlack && areRedNodeChildrenBlack(t)) 
+    case BlackTree(_, _, left, right) => List(left, right) forall areRedNodeChildrenBlack
+    case Empty => true
+  }
+  
+  def blackNodesToLeaves[A](t: Tree[A]): List[Int] = t match {
+    case Empty => List(1)
+    case BlackTree(_, _, left, right) => List(left, right) flatMap blackNodesToLeaves map (_ + 1)
+    case RedTree(_, _, left, right) => List(left, right) flatMap blackNodesToLeaves
+  }
+  
+  def areBlackNodesToLeavesEqual[A](t: Tree[A]): Boolean = t match {
+    case Empty => true
+    case ne: NonEmpty[_] => 
+      (
+        blackNodesToLeaves(ne).distinct.size == 1 
+        && areBlackNodesToLeavesEqual(ne.left) 
+        && areBlackNodesToLeavesEqual(ne.right)
+      )
+  }
+  
+  def orderIsPreserved[A](t: Tree[A]): Boolean = 
+    t.iterator zip t.iterator.drop(1) forall { case (x, y) => isSmaller(x._1, y._1) }
+    
+  def setup(invariant: Tree[Int] => Boolean) = forAll(genInput) { case (tree, parm, newTree) =>
+    invariant(newTree)
+  }
+
+  property("root is black") = setup(rootIsBlack)
+  property("all leaves are black") = setup(areAllLeavesBlack)
+  property("children of red nodes are black") = setup(areRedNodeChildrenBlack)
+  property("black nodes are balanced") = setup(areBlackNodesToLeavesEqual)
+  property("ordering of keys is preserved") = setup(orderIsPreserved)
+}
+
+object TestInsert extends RedBlackTest with RedBlackInvariants {
+  import RedBlackTest._
+  
+  override type ModifyParm = Int
+  override def genParm(tree: Tree[Int]): Gen[ModifyParm] = choose(0, tree.iterator.size + 1)
+  override def modify(tree: Tree[Int], parm: ModifyParm): Tree[Int] = tree update (generateKey(tree, parm), 0)
+
+  def generateKey(tree: Tree[Int], parm: ModifyParm): String = nodeAt(tree, parm) match {
+    case Some((key, _)) => key.init.mkString + "MN"
+    case None => nodeAt(tree, parm - 1) match {
+      case Some((key, _)) => key.init.mkString + "RN"
+      case None  => "N"
+    }
+  }
+
+  property("update adds elements") = forAll(genInput) { case (tree, parm, newTree) =>
+    treeContains(newTree, generateKey(tree, parm))
+  }
+}
+
+object TestModify extends RedBlackTest {
+  import RedBlackTest._
+  
+  def newValue = 1
+  override def minimumSize = 1
+  override type ModifyParm = Int
+  override def genParm(tree: Tree[Int]): Gen[ModifyParm] = choose(0, tree.iterator.size)
+  override def modify(tree: Tree[Int], parm: ModifyParm): Tree[Int] = nodeAt(tree, parm) map { 
+    case (key, _) => tree update (key, newValue)
+  } getOrElse tree
+
+  property("update modifies values") = forAll(genInput) { case (tree, parm, newTree) =>
+    nodeAt(tree,parm) forall { case (key, _) =>
+      newTree.iterator contains (key, newValue)
+    }
+  }
+}
+
+object TestDelete extends RedBlackTest with RedBlackInvariants  {
+  import RedBlackTest._
+
+  override def minimumSize = 1
+  override type ModifyParm = Int
+  override def genParm(tree: Tree[Int]): Gen[ModifyParm] = choose(0, tree.iterator.size)
+  override def modify(tree: Tree[Int], parm: ModifyParm): Tree[Int] = nodeAt(tree, parm) map { 
+    case (key, _) => tree delete key
+  } getOrElse tree
+  
+  property("delete removes elements") = forAll(genInput) { case (tree, parm, newTree) =>
+    nodeAt(tree, parm) forall { case (key, _) =>
+      !treeContains(newTree, key)
+    }
+  }
+}
+
+object TestRange extends RedBlackTest with RedBlackInvariants  {
+  import RedBlackTest._
+  
+  override type ModifyParm = (Option[Int], Option[Int])
+  override def genParm(tree: Tree[Int]): Gen[ModifyParm] = for {
+    from <- choose(0, tree.iterator.size)
+    to <- choose(0, tree.iterator.size) suchThat (from <=)
+    optionalFrom <- oneOf(Some(from), None, Some(from)) // Double Some(n) to get around a bug
+    optionalTo <- oneOf(Some(to), None, Some(to)) // Double Some(n) to get around a bug
+  } yield (optionalFrom, optionalTo)
+  
+  override def modify(tree: Tree[Int], parm: ModifyParm): Tree[Int] = {
+    val from = parm._1 flatMap (nodeAt(tree, _) map (_._1))
+    val to = parm._2 flatMap (nodeAt(tree, _) map (_._1))
+    tree range (from, to)
+  }
+  
+  property("range boundaries respected") = forAll(genInput) { case (tree, parm, newTree) =>
+    val from = parm._1 flatMap (nodeAt(tree, _) map (_._1))
+    val to = parm._2 flatMap (nodeAt(tree, _) map (_._1))
+    ("lower boundary" |: (from forall ( key => newTree.iterator.map(_._1) forall (key <=)))) &&
+    ("upper boundary" |: (to forall ( key => newTree.iterator.map(_._1) forall (key >))))
+  }
+  
+  property("range returns all elements") = forAll(genInput) { case (tree, parm, newTree) =>
+    val from = parm._1 flatMap (nodeAt(tree, _) map (_._1))
+    val to = parm._2 flatMap (nodeAt(tree, _) map (_._1))
+    val filteredTree = (tree.iterator
+      .map(_._1) 
+      .filter(key => from forall (key >=))
+      .filter(key => to forall (key <))
+      .toList)
+    filteredTree == newTree.iterator.map(_._1).toList
+  }
+}
+
+object Test extends Properties("RedBlack") {
+  include(TestInsert)
+  include(TestModify)
+  include(TestDelete)
+  include(TestRange)
+}
+