Fix ParVector#padTo

This was throwing a UnsupportedOperationError for small operations.

The parallel collections test suite sets `-minSuccessfulTests 5` in
test/files/scalacheck/parallel-collections/pc.scala, which is far
lower thatn the default of 100, and means that we are less likely
to falsify properties.

This parameter seems to have been added in #2476, assuming I'm reading
it correctly. Not sure of the motiviation, perhaps just to make the
slowest part of the scalacheck test suite run faster?

I haven't changed the paramater now, but instead have included a one
element collection in generator.

I also found that when the test failed, Scalacheck would try to minimize
the example, but did so assuming that the elements of the tuple of
test data could be independentally shrunk. This breaks the invariant
that the two collections contain equal elements, and led to spurious
error reports. I have disabled shrinking in all tests tests affected
by this.

6 files changed, 43 insertions, 42 deletions

diff --git a/test/files/scalacheck/parallel-collections/ParallelArrayCheck.scala b/test/files/scalacheck/parallel-collections/ParallelArrayCheck.scala
index 691a3e961e..605c16857a 100644
--- a/test/files/scalacheck/parallel-collections/ParallelArrayCheck.scala
+++ b/test/files/scalacheck/parallel-collections/ParallelArrayCheck.scala
@@ -44,7 +44,7 @@ abstract class ParallelArrayCheck[T](tp: String) extends ParallelSeqCheck[T]("Pa
     pa
   }
 
-  property("array mappings must be equal") = forAll(collectionPairs) { case (t, coll) =>
+  property("array mappings must be equal") = forAllNoShrink(collectionPairs) { case (t, coll) =>
     val results = for ((f, ind) <- mapFunctions.zipWithIndex)
       yield ("op index: " + ind) |: t.map(f) == coll.map(f)
     results.reduceLeft(_ && _)
diff --git a/test/files/scalacheck/parallel-collections/ParallelArrayViewCheck.scala b/test/files/scalacheck/parallel-collections/ParallelArrayViewCheck.scala
index 9805e2644f..fb09a5bbb7 100644
--- a/test/files/scalacheck/parallel-collections/ParallelArrayViewCheck.scala
+++ b/test/files/scalacheck/parallel-collections/ParallelArrayViewCheck.scala
@@ -46,7 +46,7 @@
 //     pa.view
 //   }
 
-//   property("forces must be equal") = forAll(collectionPairs) { case (s, coll) =>
+//   property("forces must be equal") = forAllNoShrink(collectionPairs) { case (s, coll) =>
 //     val smodif = (s ++ s).reverse.take(s.length).reverse.zip(s).drop(s.length / 2)
 //     val cmodif = (coll ++ s).reverse.take(s.length).reverse.zip(s).drop(s.length / 2).force
 //     smodif == cmodif
diff --git a/test/files/scalacheck/parallel-collections/ParallelIterableCheck.scala b/test/files/scalacheck/parallel-collections/ParallelIterableCheck.scala
index 468bcb6dd1..7e7ef2ce1b 100644
--- a/test/files/scalacheck/parallel-collections/ParallelIterableCheck.scala
+++ b/test/files/scalacheck/parallel-collections/ParallelIterableCheck.scala
@@ -109,7 +109,7 @@ abstract class ParallelIterableCheck[T](collName: String) extends Properties(col
     println("cf == tf - " + (cf == tf))
   }
 
-  property("reductions must be equal for assoc. operators") = forAll(collectionPairs) { case (t, coll) =>
+  property("reductions must be equal for assoc. operators") = forAllNoShrink(collectionPairs) { case (t, coll) =>
     if (t.size != 0) {
       val results = for ((op, ind) <- reduceOperators.zipWithIndex) yield {
         val tr = t.reduceLeft(op)
@@ -127,7 +127,7 @@ abstract class ParallelIterableCheck[T](collName: String) extends Properties(col
     } else "has size 0" |: true
   }
 
-  property("counts must be equal") = forAll(collectionPairs) { case (t, coll) =>
+  property("counts must be equal") = forAllNoShrink(collectionPairs) { case (t, coll) =>
     val results = for ((pred, ind) <- countPredicates.zipWithIndex) yield {
       val tc = t.count(pred)
       val cc = coll.count(pred)
@@ -143,19 +143,19 @@ abstract class ParallelIterableCheck[T](collName: String) extends Properties(col
     results.reduceLeft(_ && _)
   }
 
-  property("forall must be equal") = forAll(collectionPairs) { case (t, coll) =>
+  property("forall must be equal") = forAllNoShrink(collectionPairs) { case (t, coll) =>
     val results = for ((pred, ind) <- forallPredicates.zipWithIndex)
       yield ("op index: " + ind) |: t.forall(pred) == coll.forall(pred)
     results.reduceLeft(_ && _)
   }
 
-  property("exists must be equal") = forAll(collectionPairs) { case (t, coll) =>
+  property("exists must be equal") = forAllNoShrink(collectionPairs) { case (t, coll) =>
     val results = for ((pred, ind) <- existsPredicates.zipWithIndex)
       yield ("op index: " + ind) |: t.exists(pred) == coll.exists(pred)
     results.reduceLeft(_ && _)
   }
 
-  property("both must find or not find an element") = forAll(collectionPairs) { case (t, coll) =>
+  property("both must find or not find an element") = forAllNoShrink(collectionPairs) { case (t, coll) =>
     val results = for ((pred, ind) <- findPredicates.zipWithIndex) yield {
       val ft = t.find(pred)
       val fcoll = coll.find(pred)
@@ -164,7 +164,7 @@ abstract class ParallelIterableCheck[T](collName: String) extends Properties(col
     results.reduceLeft(_ && _)
   }
 
-  property("mappings must be equal") = forAll(collectionPairs) { case (t, coll) =>
+  property("mappings must be equal") = forAllNoShrink(collectionPairs) { case (t, coll) =>
     val results = for ((f, ind) <- mapFunctions.zipWithIndex) yield {
       val ms = t.map(f)
       val mp = coll.map(f)
@@ -185,7 +185,7 @@ abstract class ParallelIterableCheck[T](collName: String) extends Properties(col
     results.reduceLeft(_ && _)
   }
 
-  property("collects must be equal") = forAll(collectionPairs) { case (t, coll) =>
+  property("collects must be equal") = forAllNoShrink(collectionPairs) { case (t, coll) =>
     val results = for ((f, ind) <- partialMapFunctions.zipWithIndex) yield {
       val ps = t.collect(f)
       val pp = coll.collect(f)
@@ -201,12 +201,12 @@ abstract class ParallelIterableCheck[T](collName: String) extends Properties(col
     results.reduceLeft(_ && _)
   }
 
-  property("flatMaps must be equal") = forAll(collectionPairs) { case (t, coll) =>
+  property("flatMaps must be equal") = forAllNoShrink(collectionPairs) { case (t, coll) =>
     (for ((f, ind) <- flatMapFunctions.zipWithIndex)
       yield ("op index: " + ind) |: areEqual(t.flatMap(f), coll.flatMap(f))).reduceLeft(_ && _)
   }
 
-  property("filters must be equal") = forAll(collectionPairs) { case (t, coll) =>
+  property("filters must be equal") = forAllNoShrink(collectionPairs) { case (t, coll) =>
     (for ((p, ind) <- filterPredicates.zipWithIndex) yield {
       val tf = t.filter(p)
       val cf = coll.filter(p)
@@ -235,7 +235,7 @@ abstract class ParallelIterableCheck[T](collName: String) extends Properties(col
     }).reduceLeft(_ && _)
   }
 
-  property("filterNots must be equal") = forAll(collectionPairs) { case (t, coll) =>
+  property("filterNots must be equal") = forAllNoShrink(collectionPairs) { case (t, coll) =>
     (for ((p, ind) <- filterNotPredicates.zipWithIndex) yield {
       val tf = t.filterNot(p)
       val cf = coll.filterNot(p)
@@ -244,7 +244,7 @@ abstract class ParallelIterableCheck[T](collName: String) extends Properties(col
     }).reduceLeft(_ && _)
   }
 
-  if (!isCheckingViews) property("partitions must be equal") = forAll(collectionPairs) { case (t, coll) =>
+  if (!isCheckingViews) property("partitions must be equal") = forAllNoShrink(collectionPairs) { case (t, coll) =>
     (for ((p, ind) <- partitionPredicates.zipWithIndex) yield {
       val tpart = t.partition(p)
       val cpart = coll.partition(p)
@@ -258,15 +258,15 @@ abstract class ParallelIterableCheck[T](collName: String) extends Properties(col
     }).reduceLeft(_ && _)
   }
 
-  if (hasStrictOrder) property("takes must be equal") = forAll(collectionPairsWithLengths) { case (t, coll, n) =>
+  if (hasStrictOrder) property("takes must be equal") = forAllNoShrink(collectionPairsWithLengths) { case (t, coll, n) =>
     ("take " + n + " elements") |: t.take(n) == coll.take(n)
   }
 
-  if (hasStrictOrder) property("drops must be equal") = forAll(collectionPairsWithLengths) { case (t, coll, n) =>
+  if (hasStrictOrder) property("drops must be equal") = forAllNoShrink(collectionPairsWithLengths) { case (t, coll, n) =>
     ("drop " + n + " elements") |: t.drop(n) == coll.drop(n)
   }
 
-  if (hasStrictOrder) property("slices must be equal") = forAll(collectionPairsWith2Indices)
+  if (hasStrictOrder) property("slices must be equal") = forAllNoShrink(collectionPairsWith2Indices)
   { case (t, coll, fr, slicelength) =>
     val from = if (fr < 0) 0 else fr
     val until = if (from + slicelength > t.size) t.size else from + slicelength
@@ -290,7 +290,7 @@ abstract class ParallelIterableCheck[T](collName: String) extends Properties(col
     ("slice from " + from + " until " + until) |: tsl == collsl
   }
 
-  if (hasStrictOrder) property("splits must be equal") = forAll(collectionPairsWithLengths) { case (t, coll, n) =>
+  if (hasStrictOrder) property("splits must be equal") = forAllNoShrink(collectionPairsWithLengths) { case (t, coll, n) =>
     val tspl = t.splitAt(n)
     val cspl = coll.splitAt(n)
     if (tspl != cspl) {
@@ -303,7 +303,7 @@ abstract class ParallelIterableCheck[T](collName: String) extends Properties(col
     ("splitAt " + n) |: tspl == cspl
   }
 
-  if (hasStrictOrder) property("takeWhiles must be equal") = forAll(collectionPairs) { case (t, coll) =>
+  if (hasStrictOrder) property("takeWhiles must be equal") = forAllNoShrink(collectionPairs) { case (t, coll) =>
     (for ((pred, ind) <- takeWhilePredicates.zipWithIndex) yield {
       val tt = t.takeWhile(pred)
       val ct = coll.takeWhile(pred)
@@ -318,7 +318,7 @@ abstract class ParallelIterableCheck[T](collName: String) extends Properties(col
     }).reduceLeft(_ && _)
   }
 
-  if (hasStrictOrder) property("spans must be equal") = forAll(collectionPairs) { case (t, coll) =>
+  if (hasStrictOrder) property("spans must be equal") = forAllNoShrink(collectionPairs) { case (t, coll) =>
     (for ((pred, ind) <- spanPredicates.zipWithIndex) yield {
       val tsp = t.span(pred)
       val csp = coll.span(pred)
@@ -336,13 +336,13 @@ abstract class ParallelIterableCheck[T](collName: String) extends Properties(col
     }).reduceLeft(_ && _)
   }
 
-  if (hasStrictOrder) property("dropWhiles must be equal") = forAll(collectionPairs) { case (t, coll) =>
+  if (hasStrictOrder) property("dropWhiles must be equal") = forAllNoShrink(collectionPairs) { case (t, coll) =>
     (for ((pred, ind) <- dropWhilePredicates.zipWithIndex) yield {
       ("operator " + ind) |: t.dropWhile(pred) == coll.dropWhile(pred)
     }).reduceLeft(_ && _)
   }
 
-  property("folds must be equal for assoc. operators") = forAll(collectionPairs) { case (t, coll) =>
+  property("folds must be equal for assoc. operators") = forAllNoShrink(collectionPairs) { case (t, coll) =>
     (for (((first, op), ind) <- foldArguments.zipWithIndex) yield {
       val tres = t.foldLeft(first)(op)
       val cres = coll.fold(first)(op)
@@ -389,7 +389,7 @@ abstract class ParallelIterableCheck[T](collName: String) extends Properties(col
     }
   }
 
-  if (hasStrictOrder) property("copies to array must be equal") = forAll(collectionPairs) { case (t, coll) =>
+  if (hasStrictOrder) property("copies to array must be equal") = forAllNoShrink(collectionPairs) { case (t, coll) =>
     val tarr = newArray(t.size)
     val collarr = newArray(coll.size)
     t.copyToArray(tarr, 0, t.size)
@@ -403,7 +403,7 @@ abstract class ParallelIterableCheck[T](collName: String) extends Properties(col
     tarr.toSeq == collarr.toSeq
   }
 
-  if (hasStrictOrder) property("scans must be equal") = forAll(collectionPairs) {
+  if (hasStrictOrder) property("scans must be equal") = forAllNoShrink(collectionPairs) {
     case (t, coll) =>
       (for (((first, op), ind) <- foldArguments.zipWithIndex) yield {
         val tscan = t.scanLeft(first)(op)
@@ -419,7 +419,7 @@ abstract class ParallelIterableCheck[T](collName: String) extends Properties(col
       }).reduceLeft(_ && _)
   }
 
-  property("groupBy must be equal") = forAll(collectionPairs) {
+  property("groupBy must be equal") = forAllNoShrink(collectionPairs) {
     case (t, coll) =>
       (for ((f, ind) <- groupByFunctions.zipWithIndex) yield {
         val tgroup = t.groupBy(f)
diff --git a/test/files/scalacheck/parallel-collections/ParallelMapCheck1.scala b/test/files/scalacheck/parallel-collections/ParallelMapCheck1.scala
index d4643e7f2c..50aa4ad0c7 100644
--- a/test/files/scalacheck/parallel-collections/ParallelMapCheck1.scala
+++ b/test/files/scalacheck/parallel-collections/ParallelMapCheck1.scala
@@ -17,7 +17,7 @@ import scala.collection.parallel._
 abstract class ParallelMapCheck[K, V](collname: String) extends ParallelIterableCheck[(K, V)](collname) {
   type CollType <: ParMap[K, V]
 
-  property("gets iterated keys") = forAll(collectionPairs) {
+  property("gets iterated keys") = forAllNoShrink(collectionPairs) {
     case (t, coll) =>
     val containsT = for ((k, v) <- t) yield (coll.get(k) == Some(v))
     val containsSelf = coll.map { case (k, v) => coll.get(k) == Some(v) }
diff --git a/test/files/scalacheck/parallel-collections/ParallelSeqCheck.scala b/test/files/scalacheck/parallel-collections/ParallelSeqCheck.scala
index 3f8a8ad4f5..48c3d3f745 100644
--- a/test/files/scalacheck/parallel-collections/ParallelSeqCheck.scala
+++ b/test/files/scalacheck/parallel-collections/ParallelSeqCheck.scala
@@ -24,6 +24,7 @@ abstract class ParallelSeqCheck[T](collName: String) extends ParallelIterableChe
   def fromSeq(s: Seq[T]): CollType
 
   override def instances(vals: Seq[Gen[T]]): Gen[Seq[T]] = oneOf(
+    Gen.const(ofSize(vals, 1)),
     sized(
       sz =>
       ofSize(vals, sz)
@@ -74,7 +75,7 @@ abstract class ParallelSeqCheck[T](collName: String) extends ParallelIterableChe
     coll.patch(updateStart, coll, howMany)
   }
 
-  property("segmentLengths must be equal") = forAll(collectionPairsWithLengths) { case (s, coll, len) =>
+  property("segmentLengths must be equal") = forAllNoShrink(collectionPairsWithLengths) { case (s, coll, len) =>
     (for ((pred, ind) <- segmentLengthPredicates.zipWithIndex) yield {
       val slen = s.segmentLength(pred, if (len < 0) 0 else len)
       val clen = coll.segmentLength(pred, len)
@@ -88,13 +89,13 @@ abstract class ParallelSeqCheck[T](collName: String) extends ParallelIterableChe
     }).reduceLeft(_ && _)
   }
 
-  property("prefixLengths must be equal") = forAll(collectionPairs) { case (s, coll) =>
+  property("prefixLengths must be equal") = forAllNoShrink(collectionPairs) { case (s, coll) =>
     (for ((pred, ind) <- segmentLengthPredicates.zipWithIndex) yield {
       ("operator " + ind) |: s.prefixLength(pred) == coll.prefixLength(pred)
     }).reduceLeft(_ && _)
   }
 
-  property("indexWheres must be equal") = forAll(collectionPairsWithLengths) { case (s, coll, len) =>
+  property("indexWheres must be equal") = forAllNoShrink(collectionPairsWithLengths) { case (s, coll, len) =>
     (for ((pred, ind) <- indexWherePredicates.zipWithIndex) yield {
       val sind = s.indexWhere(pred, len)
       val cind = coll.indexWhere(pred, len)
@@ -109,7 +110,7 @@ abstract class ParallelSeqCheck[T](collName: String) extends ParallelIterableChe
     }).reduceLeft(_ && _)
   }
 
-  property("lastIndexWheres must be equal") = forAll(collectionPairsWithLengths) { case (s, coll, len) =>
+  property("lastIndexWheres must be equal") = forAllNoShrink(collectionPairsWithLengths) { case (s, coll, len) =>
     (for ((pred, ind) <- lastIndexWherePredicates.zipWithIndex) yield {
       val end = if (len >= s.size) s.size - 1 else len
       val sind = s.lastIndexWhere(pred, end)
@@ -118,7 +119,7 @@ abstract class ParallelSeqCheck[T](collName: String) extends ParallelIterableChe
     }).reduceLeft(_ && _)
   }
 
-  property("reverses must be equal") = forAll(collectionPairs) { case (s, coll) =>
+  property("reverses must be equal") = forAllNoShrink(collectionPairs) { case (s, coll) =>
     (s.length == 0 && s.getClass == classOf[collection.immutable.Range]) ||
     {
       val sr = s.reverse
@@ -133,13 +134,13 @@ abstract class ParallelSeqCheck[T](collName: String) extends ParallelIterableChe
     }
   }
 
-  property("reverseMaps must be equal") = forAll(collectionPairs) { case (s, coll) =>
+  property("reverseMaps must be equal") = forAllNoShrink(collectionPairs) { case (s, coll) =>
     (for ((f, ind) <- reverseMapFunctions.zipWithIndex) yield {
       ("operator " + ind) |: s.reverseMap(f) == coll.reverseMap(f)
     }).reduceLeft(_ && _)
   }
 
-  property("sameElements must be equal") = forAll(collectionPairsWithModifiedWithLengths) {
+  property("sameElements must be equal") = forAllNoShrink(collectionPairsWithModifiedWithLengths) {
   case (s, coll, collmodif, len) =>
     val pos = if (len < 0) 0 else len
     val scm = s.sameElements(collmodif)
@@ -171,7 +172,7 @@ abstract class ParallelSeqCheck[T](collName: String) extends ParallelIterableChe
     }).reduceLeft(_ && _)
   }
 
-  property("startsWiths must be equal") = forAll(collectionPairsWithModifiedWithLengths) {
+  property("startsWiths must be equal") = forAllNoShrink(collectionPairsWithModifiedWithLengths) {
   case (s, coll, collmodif, len) =>
     val pos = if (len < 0) 0 else len
     ("start with self" |: s.startsWith(s) == coll.startsWith(coll)) &&
@@ -195,7 +196,7 @@ abstract class ParallelSeqCheck[T](collName: String) extends ParallelIterableChe
     }).reduceLeft(_ && _)
   }
 
-  property("endsWiths must be equal") = forAll(collectionPairsWithModified) {
+  property("endsWiths must be equal") = forAllNoShrink(collectionPairsWithModified) {
   case (s, coll, collmodif) =>
     ("ends with self" |: s.endsWith(s) == coll.endsWith(s)) &&
     ("ends with tail" |: (s.length == 0 || s.endsWith(s.tail) == coll.endsWith(coll.tail))) &&
@@ -214,7 +215,7 @@ abstract class ParallelSeqCheck[T](collName: String) extends ParallelIterableChe
     }).reduceLeft(_ && _)
   }
 
-  property("unions must be equal") = forAll(collectionPairsWithModified) { case (s, coll, collmodif) =>
+  property("unions must be equal") = forAllNoShrink(collectionPairsWithModified) { case (s, coll, collmodif) =>
     ("modified" |: s.union(collmodif.seq) == coll.union(collmodif)) &&
     ("empty" |: s.union(Nil) == coll.union(fromSeq(Nil)))
   }
@@ -233,7 +234,7 @@ abstract class ParallelSeqCheck[T](collName: String) extends ParallelIterableChe
     ("with one" |: (s.length == 0 || s.patch(from, List(s(0)), 1) == coll.patch(from, fromSeq(List(coll(0))), 1)))
   }
 
-  if (!isCheckingViews) property("updates must be equal") = forAll(collectionPairsWithLengths) { case (s, coll, len) =>
+  if (!isCheckingViews) property("updates must be equal") = forAllNoShrink(collectionPairsWithLengths) { case (s, coll, len) =>
     val pos = if (len >= s.length) s.length - 1 else len
     if (s.length > 0) {
       val supd = s.updated(pos, s(0))
@@ -248,15 +249,15 @@ abstract class ParallelSeqCheck[T](collName: String) extends ParallelIterableChe
     } else "trivially" |: true
   }
 
-  property("prepends must be equal") = forAll(collectionPairs) { case (s, coll) =>
+  property("prepends must be equal") = forAllNoShrink(collectionPairs) { case (s, coll) =>
     s.length == 0 || s(0) +: s == coll(0) +: coll
   }
 
-  property("appends must be equal") = forAll(collectionPairs) { case (s, coll) =>
+  property("appends must be equal") = forAllNoShrink(collectionPairs) { case (s, coll) =>
     s.length == 0 || s :+ s(0) == coll :+ coll(0)
   }
 
-  property("padTos must be equal") = forAll(collectionPairsWithLengths) { case (s, coll, len) =>
+  property("padTos must be equal") = forAllNoShrink(collectionPairsWithLengths) { case (s, coll, len) =>
     val someValue = sampleValue
     val sdoub = s.padTo(len * 2, someValue)
     val cdoub = coll.padTo(len * 2, someValue)
@@ -267,10 +268,10 @@ abstract class ParallelSeqCheck[T](collName: String) extends ParallelIterableChe
       println(cdoub)
     }
     ("smaller" |: s.padTo(len / 2, someValue) == coll.padTo(len / 2, someValue)) &&
-    ("bigger" |: sdoub == cdoub)
+      ("bigger" |: sdoub == cdoub)
   }
 
-  property("corresponds must be equal") = forAll(collectionPairsWithModified) { case (s, coll, modified) =>
+  property("corresponds must be equal") = forAllNoShrink(collectionPairsWithModified) { case (s, coll, modified) =>
     val modifcut = modified.toSeq.slice(0, modified.length)
     ("self" |: s.corresponds(s)(_ == _) == coll.corresponds(coll)(_ == _)) &&
     ("modified" |: s.corresponds(modified.seq)(_ == _) == coll.corresponds(modified)(_ == _)) &&
diff --git a/test/files/scalacheck/parallel-collections/ParallelSetCheck.scala b/test/files/scalacheck/parallel-collections/ParallelSetCheck.scala
index 56f7832fed..c22dddf96d 100644
--- a/test/files/scalacheck/parallel-collections/ParallelSetCheck.scala
+++ b/test/files/scalacheck/parallel-collections/ParallelSetCheck.scala
@@ -17,7 +17,7 @@ import scala.collection.parallel._
 abstract class ParallelSetCheck[T](collname: String) extends ParallelIterableCheck[T](collname) {
   type CollType <: ParSet[T]
 
-  property("gets iterated keys") = forAll(collectionPairs) {
+  property("gets iterated keys") = forAllNoShrink(collectionPairs) {
     case (t, coll) =>
     val containsT = for (elem <- t) yield (coll.contains(elem))
     val containsSelf = for (elem <- coll) yield (coll.contains(elem))