Initial implementation of lazily evaluated sequences

libraries/stdlib/test/sequences/SequenceTest.kt

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+package test.sequences
+
+import java.util.ArrayList
+
+import kotlin.sequences.asSequence
+import kotlin.sequences.sequence
+import kotlin.util.arrayList
+import kotlin.util.fold
+
+import kotlin.test.assertEquals
+import org.junit.Test
+
+class SequenceTest {
+
+  Test fun filterReturnsTheExpectedSequence() {
+    val actual = (1..10).asSequence().filter { it % 2 == 0 }.toList()
+    assertEquals(arrayList(2, 4, 6, 8, 10), actual)
+  }
+
+  Test fun filterReturnsAnEmptySequenceWhenNoElementMatchesThePredicate() {
+    val actual = sequence(1, 3, 4, 7).filter { it > 7 }.toList()
+    assertEquals(ArrayList<Int>(), actual)
+  }
+
+  Test fun foldReturnsTheExpectedReduction() {
+    val actual = (1..10).asSequence().filter { it % 2 == 1 }.fold(0, sum)
+    assertEquals(1 + 3 + 5 + 7 + 9, actual)
+  }
+
+  Test fun foldReturnsTheInitialValueForAnEmptySequence() {
+    val initialValue = 0
+    val actual = (1..0).asSequence().fold(initialValue, sum)
+
+    assertEquals(initialValue, actual)
+  }
+
+  Test fun mapReturnsTheExpectedTransformation() {
+    val actual = sequence(1, 3, 4, 7).map { it * 2 }.toList()
+    assertEquals(arrayList(2, 6, 8, 14), actual)
+  }
+
+  Test fun takeReturnsTheFirstNElements() {
+    var actual = (1..5).asSequence().take(3).toList()
+    assertEquals(arrayList(1, 2, 3), actual)
+  }
+
+  Test fun takeReturnsTheEntireSequenceWhenTheNumberOfElementsIsGreaterThanItsSize() {
+    val actual = sequence(1, 2).take(3).toList()
+    assertEquals(arrayList(1, 2), actual)
+  }
+
+  Test fun takeReturnsAnEmptySequenceForAnEmptySequence() {
+    val actual = (1..0).asSequence().take(3).toList()
+    assertEquals(ArrayList<Int>(), actual)
+  }
+
+  Test fun takeReturnsAnEmptySequenceWhenTheNumberOfElementsToExtractIsZero() {
+    val actual = sequence(1, 2).take(0).toList()
+    assertEquals(ArrayList<Int>(), actual)
+  }
+
+  Test fun takeReturnsAnEmptySequenceWhenTheNumberOfElementsToExtractIsNegative() {
+    val actual = sequence(1, 2).take(-1).toList()
+    assertEquals(ArrayList<Int>(), actual)
+  }
+
+  Test fun takeWhileReturnsTheFirstElementsMatchingAGivenPredicate() {
+    val actual = sequence(1, 2, 3, 4, 1, 2, 3, 4).takeWhile { it < 3 }.toList()
+    assertEquals(arrayList(1, 2), actual)
+  }
+
+  Test fun takeWhileReturnsTheEntireSequenceWhenThePredicateMatchesAllElements() {
+    val actual = sequence(1, 2, 3).takeWhile { it < 9 }.toList()
+    assertEquals(arrayList(1, 2, 3), actual)
+  }
+
+  Test fun takeWhileReturnsAnEmptySequenceWhenThePredicateMatchesNothing() {
+    val actual = sequence(1, 2, 3).takeWhile { it < 0 }.toList()
+    assertEquals(ArrayList<Int>(), actual)
+  }
+
+  private val sum = { (a : Int, b : Int) -> a + b }
+}