more SliceSpec tests

core/src/main/scala/swaydb/core/segment/merge/SegmentGrouper.scala

@@ -82,7 +82,7 @@ private[merge] object SegmentGrouper extends LazyLogging {
     if (shouldGroupGroups(segmentKeyValues = keyValues, groupingStrategy = groupingStrategy, force = force)) {
       //use segmentKeyValues.last.stats.position instead of keyValues.size because position is pre-calculated.
       val keyValuesToGroup = Slice.create[KeyValue.WriteOnly](keyValues.last.stats.position)
-      //do not need to recalculate stats since all key-values are being groups.
+      //do not need to recalculate stats since all key-values are being grouped.
       //      keyValues foreach (keyValuesToGroup add _.updateStats(bloomFilterFalsePositiveRate, keyValuesToGroup.lastOption))
       keyValues foreach (keyValuesToGroup add _)
       Some(keyValuesToGroup)
@@ -99,7 +99,7 @@ private[merge] object SegmentGrouper extends LazyLogging {
   private def keyValuesToGroup(segmentKeyValues: Iterable[KeyValue.WriteOnly],
                                bloomFilterFalsePositiveRate: Double,
                                groupingStrategy: KeyValueGroupingStrategyInternal,
-                               force: Boolean): Try[Option[(Iterable[KeyValue.WriteOnly], Option[Transient.Group])]] =
+                               force: Boolean): Try[Option[(Slice[KeyValue.WriteOnly], Option[Transient.Group])]] =
     if (shouldGroupKeyValues(segmentKeyValues = segmentKeyValues, groupingStrategy = groupingStrategy, force = force)) {
       //create a new list of key-values with stats updated.
       val expectedGroupsKeyValueCount = segmentKeyValues.last.stats.position - segmentKeyValues.last.stats.groupsCount

data/src/main/scala/swaydb/data/slice/Slice.scala

@@ -246,7 +246,7 @@ object Slice {
 
   class SliceBuilder[T: ClassTag](sizeHint: Int) extends mutable.Builder[T, Slice[T]] {
     //max is used to in-case sizeHit == 0 which is possible for cases where (None ++ Some(Slice[T](...)))
-    protected var slice: Slice[T] = Slice.create[T](((sizeHint max 16) * 2.5).toInt)
+    protected var slice: Slice[T] = Slice.create[T](((sizeHint max 100) * 2.5).toInt)
 
     def extendSlice(by: Int) = {
       val extendedSlice = Slice.create[T](slice.size * by)
@@ -277,7 +277,7 @@ object Slice {
   implicit def canBuildFrom[T: ClassTag]: CanBuildFrom[Slice[_], T, Slice[T]] =
     new CanBuildFrom[Slice[_], T, Slice[T]] {
       def apply(from: Slice[_]) =
-        new SliceBuilder[T](from.size max 16) //max is used in-case from.size == 0
+        new SliceBuilder[T](from.size max 100) //max is used in-case from.size == 0
 
       def apply() =
         new SliceBuilder[T](100)
@@ -518,7 +518,7 @@ class Slice[+T: ClassTag](array: Array[T],
     array.length
 
   override protected[this] def newBuilder: scala.collection.mutable.Builder[T, Slice[T]] =
-    new Slice.SliceBuilder[T](100)
+    new Slice.SliceBuilder[T](array.length max 100)
 
   override def equals(that: Any): Boolean =
     that match {

data/src/test/scala/swaydb/data/slice/SliceSpec.scala

@@ -401,4 +401,35 @@ class SliceSpec extends WordSpec with Matchers {
         .addAll(Slice(3, 4))
     }
   }
+
+  "None ++ Some(Slice[T](...))" in {
+    val merged: Iterable[Slice[Int]] = Some(Slice[Int](1, 2, 3)) ++ None
+    merged.flatten
+      .toList should contain inOrderOnly(1, 2, 3)
+  }
+
+  "++ empty slices" in {
+    val merged: Slice[Int] = Slice.empty[Int] ++ Slice.empty[Int]
+    merged shouldBe empty
+    merged.written shouldBe 0
+    merged.isEmpty shouldBe true
+    merged.isFull shouldBe true
+  }
+
+  "++ empty and non empty slices" in {
+    val merged: Slice[Int] = Slice.empty[Int] ++ Slice(1)
+    merged should contain only 1
+    merged.written shouldBe 1
+    merged.isEmpty shouldBe false
+    merged.isFull shouldBe true
+  }
+
+  "++ non empty and empty slices" in {
+    val merged: Slice[Int] = Slice(1) ++ Slice.empty[Int]
+    merged should contain only 1
+    merged.written shouldBe 1
+    merged.isEmpty shouldBe false
+    merged.isFull shouldBe true
+  }
+
 }