Kotlin split list in pairs examples. (#6368)

* Kotlin split list in pairs examples.

* Renamed some items.

core-kotlin/src/test/kotlin/com/baeldung/splitting/SplittingTest.kt

@@ -0,0 +1,99 @@
+package com.baeldung.lambda
+
+import org.junit.jupiter.api.Test
+import kotlin.test.assertEquals
+
+class SplittingTest {
+    private val evenList = listOf(0, "a", 1, "b", 2, "c");
+
+    private val unevenList = listOf(0, "a", 1, "b", 2, "c", 3);
+
+    private fun verifyList(resultList: List<List<Any>>) {
+        assertEquals("[[0, a], [1, b], [2, c]]", resultList.toString())
+    }
+
+    private fun verifyPartialList(resultList: List<List<Any>>) {
+        assertEquals("[[0, a], [1, b], [2, c], [3]]", resultList.toString())
+    }
+
+    @Test
+    fun whenChunked_thenListIsSplit() {
+        val resultList = evenList.chunked(2)
+        verifyList(resultList)
+    }
+
+    @Test
+    fun whenUnevenChunked_thenListIsSplit() {
+        val resultList = unevenList.chunked(2)
+        verifyPartialList(resultList)
+    }
+
+    @Test
+    fun whenWindowed_thenListIsSplit() {
+        val resultList = evenList.windowed(2, 2)
+        verifyList(resultList)
+    }
+
+    @Test
+    fun whenUnevenPartialWindowed_thenListIsSplit() {
+        val resultList = unevenList.windowed(2, 2, partialWindows = true)
+        verifyPartialList(resultList)
+    }
+
+    @Test
+    fun whenUnevenWindowed_thenListIsSplit() {
+        val resultList = unevenList.windowed(2, 2, partialWindows = false)
+        verifyList(resultList)
+    }
+
+    @Test
+    fun whenGroupByWithAscendingNumbers_thenListIsSplit() {
+        val numberList = listOf(1, 2, 3, 4, 5, 6);
+        val resultList = numberList.groupBy { (it + 1) / 2 }
+        assertEquals("[[1, 2], [3, 4], [5, 6]]", resultList.values.toString())
+        assertEquals("[1, 2, 3]", resultList.keys.toString())
+    }
+
+    @Test
+    fun whenGroupByWithAscendingNumbersUneven_thenListIsSplit() {
+        val numberList = listOf(1, 2, 3, 4, 5, 6, 7);
+        val resultList = numberList.groupBy { (it + 1) / 2 }.values
+        assertEquals("[[1, 2], [3, 4], [5, 6], [7]]", resultList.toString())
+    }
+
+    @Test
+    fun whenGroupByWithRandomNumbers_thenListIsSplitInWrongWay() {
+        val numberList = listOf(1, 3, 8, 20, 23, 30);
+        val resultList = numberList.groupBy { (it + 1) / 2 }
+        assertEquals("[[1], [3], [8], [20], [23], [30]]", resultList.values.toString())
+        assertEquals("[1, 2, 4, 10, 12, 15]", resultList.keys.toString())
+    }
+
+    @Test
+    fun whenWithIndexGroupBy_thenListIsSplit() {
+        val resultList = evenList.withIndex()
+                .groupBy { it.index / 2 }
+                .map { it.value.map { it.value } }
+        verifyList(resultList)
+    }
+
+    @Test
+    fun whenWithIndexGroupByUneven_thenListIsSplit() {
+        val resultList = unevenList.withIndex()
+                .groupBy { it.index / 2 }
+                .map { it.value.map { it.value } }
+        verifyPartialList(resultList)
+    }
+
+    @Test
+    fun whenFoldIndexed_thenListIsSplit() {
+        val resultList = evenList.foldIndexed(ArrayList<ArrayList<Any>>(evenList.size / 2)) { index, acc, item ->
+            if (index % 2 == 0) {
+                acc.add(ArrayList(2))
+            }
+            acc.last().add(item)
+            acc
+        }
+        verifyList(resultList)
+    }
+}