Merge pull request #1412 from yadavan88/dropwhile-takewhile

dropWhile and takeWhile in Scala

Author: dominiqueplante

scala-core-collections-modules/scala-core-collections-4/src/test/scala/com/baeldung/scala/takewhiledropwhile/TakeWhileDropWhileUnitTest.scala

@@ -0,0 +1,47 @@
+package com.baeldung.scala.takewhiledropwhile
+
+import org.scalatest.matchers.should.Matchers
+import org.scalatest.wordspec.AnyWordSpec
+
+class TakeWhileDropWhileUnitTest extends AnyWordSpec with Matchers {
+
+  private val numbersAscending = List(1, 2, 3, 4, 5, 6, 7, 8)
+  private val numbersDescending = List(8, 7, 6, 5, 4, 3, 2, 1)
+  private val numbersMixed = List(1, 2, 3, 4, 3, 2, 1)
+
+  "takeWhile" should {
+    "take element from list till condition satisfies" in {
+      val lessThanFive = numbersAscending.takeWhile(_ < 5)
+      lessThanFive shouldBe List(1, 2, 3, 4)
+    }
+
+    "return different elements when the element order changes" in {
+      val lessThanFive = numbersDescending.takeWhile(_ < 5)
+      lessThanFive shouldBe Nil
+    }
+
+    "stop taking as soon as the first failure in predicate" in {
+      val lessThanThree = numbersMixed.takeWhile(_ < 3)
+      lessThanThree shouldBe List(1, 2)
+    }
+
+    "take all elements if the predicate is satisfied for all" in {
+      val positive = numbersAscending.takeWhile(_ > 0)
+      positive shouldBe numbersAscending
+    }
+
+  }
+
+  "dropWhile" should {
+    "drop the elements from the list until the predicate is true" in {
+      val dropLessThan5 = numbersAscending.dropWhile(_ < 5)
+      dropLessThan5 shouldBe List(5, 6, 7, 8)
+    }
+
+    "dropWhile behavior changes with the order" in {
+      val dropLessThan5 = numbersDescending.dropWhile(_ < 5)
+      dropLessThan5 shouldBe numbersDescending
+    }
+  }
+
+}