feat(#12): add element's updating in NotEmptyMutableList

src/main/kotlin/kotools/types/collections/NotEmptyMutableList.kt

@@ -113,5 +113,16 @@ public class NotEmptyMutableList<E>(override var head: E, vararg tail: E) :
 
     override fun get(index: Int): E = if (index == 0) head else tail[index - 1]
     override fun removeAt(index: Int): E = TODO("Not implemented yet")
-    override fun set(index: Int, element: E): E = TODO("Not implemented yet")
+
+    /**
+     * Replaces the element at the specified [index] in this list with the
+     * specified [element], or throws an [IndexOutOfBoundsException] if the
+     * [index] is out of bounds.
+     */
+    @Throws(IndexOutOfBoundsException::class)
+    override fun set(index: Int, element: E): E = when (index) {
+        in 1 until size -> element.also { tail[index - 1] = it }
+        0 -> element.also { head = it }
+        else -> indexOutOfBounds(index, size)
+    }
 }

src/test/kotlin/kotools/types/collections/NotEmptyMutableListTest.kt

@@ -176,7 +176,80 @@ class NotEmptyMutableListTest {
     inner class RemoveAt // TODO: 21/07/2022 Not implemented yet
 
     @Nested
-    inner class Set // TODO: 21/07/2022 Not implemented yet
+    inner class Set {
+        @Test
+        fun `should replace the head with an index that equals 0`() {
+            // GIVEN
+            val expectedList: NotEmptyList<String> =
+                NotEmptyList("one", "two", "three")
+            val index = 0
+            val previousElement = "four"
+            val list: NotEmptyMutableList<String> = expectedList
+                .subList(1, expectedList.size)
+                .toNotEmptyMutableList()
+                .apply { add(index, previousElement) }
+            val element: String = expectedList.head
+            // WHEN
+            assertDoesNotThrow { list[index] = element }
+            // THEN
+            list.run {
+                head assertEquals element
+                head assertNotEquals previousElement
+                this[index] assertEquals element
+                this[index] assertNotEquals previousElement
+                size assertEquals expectedList.size
+                forEachIndexed { index2: Int, element2: String ->
+                    element2 assertEquals expectedList[index2]
+                }
+            }
+        }
+
+        @Test
+        fun `should replace a tail's element with an index in 1 until the list's size`() {
+            // GIVEN
+            val expectedList: NotEmptyList<String> =
+                NotEmptyList("one", "two", "three")
+            val previousElement = "four"
+            val list: NotEmptyMutableList<String> = NotEmptyMutableList(
+                expectedList.head,
+                previousElement,
+                expectedList.last()
+            )
+            val index = 1
+            val element: String = expectedList[index]
+            // WHEN
+            assertDoesNotThrow { list[index] = element }
+            // THEN
+            list.run {
+                this[index] assertEquals element
+                this[index] assertNotEquals previousElement
+                size assertEquals expectedList.size
+                forEachIndexed { index2: Int, element2: String ->
+                    element2 assertEquals expectedList[index2]
+                }
+            }
+        }
+
+        @Test
+        fun `should throw an error with an index that is out of bounds`() {
+            // GIVEN
+            val expectedList: NotEmptyList<String> =
+                NotEmptyList("one", "two", "three")
+            val list: NotEmptyMutableList<String> =
+                expectedList.toNotEmptyMutableList()
+            val index = list.size
+            val element = "error"
+            // WHEN
+            assertFailsWith<IndexOutOfBoundsException> { list[index] = element }
+            // THEN
+            list.run {
+                size assertEquals expectedList.size
+                forEachIndexed { index2: Int, element2: String ->
+                    element2 assertEquals expectedList[index2]
+                }
+            }
+        }
+    }
 
     // ---------- Conversions ----------