[iter-add-at-idx] add elements to list while iterating (#768)

Author: sk1418

core-kotlin-modules/core-kotlin-collections-list-2/src/test/kotlin/iterateListAndAddItem/IterateListAndAddElementUnitTest.kt

@@ -0,0 +1,101 @@
+package iterateListAndAddItem
+
+import org.junit.jupiter.api.Test
+import kotlin.test.assertEquals
+
+
+fun byForEach(list: List<String>): List<String> {
+    val result = mutableListOf<String>()
+    list.forEach {
+        result += it
+        if (it.length > 1) {
+            result += "<- a long one"
+        }
+    }
+    return result.toList()
+}
+
+fun byBuildList(list: List<String>) =
+    buildList {
+        list.forEach {
+            this += it
+            if (it.length > 1) {
+                this += "<- a long one"
+            }
+        }
+    }
+
+fun addBeforeByBuildList(list: List<String>) =
+    buildList {
+        list.forEach {
+            if (it.length > 1) {
+                this += "a long one ->"
+            }
+            this += it
+        }
+    }
+
+fun byListIterator(list: MutableList<String>) {
+    val it = list.listIterator()
+    for (e in it) {
+        if (e.length > 1) {
+            it.add("<- a long one")
+        }
+    }
+}
+
+fun addBeforeByListIterator(list: MutableList<String>) {
+    val it = list.listIterator()
+    for (e in it) {
+        if (e.length > 1) {
+            it.previous()
+            it.add("a long one ->")
+            it.next()
+        }
+    }
+}
+
+class IterateListAndAddElementUnitTest {
+    val myList = listOf("ab", "a", "cd", "c", "xyz")
+
+    @Test
+    fun `when using byLoop() then get expected result`() {
+        assertEquals(
+            listOf("ab", "<- a long one", "a", "cd", "<- a long one", "c", "xyz", "<- a long one"),
+            byForEach(myList)
+        )
+    }
+
+    @Test
+    fun `when using buildList() then get expected result`() {
+        assertEquals(
+            listOf("ab", "<- a long one", "a", "cd", "<- a long one", "c", "xyz", "<- a long one"),
+            byBuildList(myList)
+        )
+        //insert before the target
+        assertEquals(
+            listOf("a long one ->", "ab", "a", "a long one ->", "cd", "c", "a long one ->", "xyz"),
+            addBeforeByBuildList(myList)
+        )
+    }
+
+    @Test
+    fun `given mutableList, when using listIterator to append elements then get expected result`() {
+        val myMutableList = mutableListOf("ab", "a", "cd", "c", "xyz")
+        byListIterator(myMutableList)
+        assertEquals(
+            listOf("ab", "<- a long one", "a", "cd", "<- a long one", "c", "xyz", "<- a long one"),
+            myMutableList
+        )
+    }
+
+    @Test
+    fun `given mutableList, when using listIterator to prepend elements then get expected result`() {
+        val myMutableList = mutableListOf("ab", "a", "cd", "c", "xyz")
+        addBeforeByListIterator(myMutableList)
+        assertEquals(
+            listOf("a long one ->", "ab", "a", "a long one ->", "cd", "c", "a long one ->", "xyz"),
+            myMutableList
+        )
+    }
+}