Release 3.1.5: remove debug println, drop worksheet leftover, modernize CI

- Remove stray println(child.value) from TreeNode.removeChild()
- Add regression test for removeChild() return value
- Delete leftover ExampleUnitTest.kt template test
- Remove Example.ws.kts worksheet and kotlin("script-runtime") from jvmMain
- Bump actions/checkout v2 -> v4 in CI workflows
- Update README install snippets to 3.1.5
- Bump version to 3.1.5

src/commonMain/kotlin/com.github.adriankuta/datastructure/tree/TreeNode.kt

@@ -62,7 +62,6 @@ open class TreeNode<T>(val value: T, var treeIterator: TreeNodeIterators = PreOr
      * @return `true` if the node has been successfully removed; `false` if it was not present in the tree.
      */
     fun removeChild(child: TreeNode<T>): Boolean {
-        println(child.value)
         val removed = child._parent?._children?.remove(child)
         child._parent = null
         return removed ?: false

src/commonTest/kotlin/com.github.adriankuta/datastructure.tree/ExampleUnitTest.kt

@@ -1,16 +0,0 @@
-package com.github.adriankuta.datastructure.tree
-
-import kotlin.test.Test
-import kotlin.test.assertEquals
-
-/**
- * Example local unit test, which will execute on the development machine (host).
- *
- * See [testing documentation](http://d.android.com/tools/testing).
- */
-class ExampleUnitTest {
-    @Test
-    fun addition_isCorrect() {
-        assertEquals(4, 2 + 2)
-    }
-}

src/commonTest/kotlin/com.github.adriankuta/datastructure.tree/TreeNodeTest.kt

@@ -4,7 +4,9 @@ import com.github.adriankuta.datastructure.tree.iterators.TreeNodeIterators
 import kotlin.test.Test
 import kotlin.test.assertContentEquals
 import kotlin.test.assertEquals
+import kotlin.test.assertFalse
 import kotlin.test.assertNull
+import kotlin.test.assertTrue
 
 class TreeNodeTest {
 
@@ -62,6 +64,18 @@ class TreeNodeTest {
         )
     }
 
+    @Test
+    fun removeChildReturnsTrueWhenPresentFalseOtherwise() {
+        val root = TreeNode("Root")
+        val child = TreeNode("Child")
+        root.addChild(child)
+
+        assertTrue(root.removeChild(child), "Removing a present child returns true")
+        assertFalse(root.removeChild(child), "Removing an already-removed child returns false")
+        assertNull(child.parent, "Removed child is detached from its parent")
+        assertEquals(emptyList(), root.children)
+    }
+
     @Test
     fun clearTest() {
         val root = TreeNode("Root")

src/jvmMain/kotlin/Example.ws.kts

@@ -1,14 +0,0 @@
-import com.github.adriankuta.datastructure.tree.tree
-
-val root =
-    tree("World") {
-        child("North America") {
-            child("USA")
-        }
-        child("Europe") {
-            child("Poland")
-            child("Germany")
-        }
-    }
-
-print(root.prettyString())