First version of Iterator vs For Loop unit testing (#15365)

* First version of Iterator vs For Loop unit testing

* Add a new line after package

* Update the method name

core-java-modules/core-java-collections-5/src/test/java/com/baeldung/iteratorvsforloop/IteratorForLoopUnitTest.java

@@ -0,0 +1,129 @@
+package com.baeldung.iteratorvsforloop;
+
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.*;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.ConcurrentModificationException;
+import java.util.List;
+import java.util.Iterator;
+import java.util.Collections;
+import java.util.ListIterator;
+
+public class IteratorForLoopUnitTest {
+
+    @Test
+    public void givenEmptyCollection_whenUsingForLoop_thenNoElementsAreIterated() {
+        List<String> names = Collections.emptyList();
+        StringBuilder stringBuilder = new StringBuilder();
+
+        for (int i = 0; i < names.size(); i++) {
+            stringBuilder.append(names.get(i));
+        }
+
+        assertEquals("", stringBuilder.toString());
+    }
+
+    @Test
+    public void givenEmptyCollection_whenUsingIterator_thenNoElementsAreIterated() {
+        List<String> names = Collections.emptyList();
+        StringBuilder stringBuilder = new StringBuilder();
+
+        Iterator<String> iterator = names.iterator();
+        while (iterator.hasNext()) {
+            stringBuilder.append(iterator.next());
+        }
+
+        assertEquals("", stringBuilder.toString());
+    }
+
+
+    @Test
+    public void givenCollectionWithElements_whenUsingForLoop_thenAllElementsAreIterated() {
+        List<String> names = Arrays.asList("Alice", "Bob", "Charlie");
+        StringBuilder stringBuilder = new StringBuilder();
+
+        for (int i = 0; i < names.size(); i++) {
+            stringBuilder.append(names.get(i));
+        }
+
+        assertEquals("AliceBobCharlie", stringBuilder.toString());
+    }
+
+    @Test
+    public void givenCollectionWithElements_whenUsingIterator_thenAllElementsAreIterated() {
+        List<String> names = Arrays.asList("Alice", "Bob", "Charlie");
+        StringBuilder stringBuilder = new StringBuilder();
+
+        Iterator<String> iterator = names.iterator();
+        while (iterator.hasNext()) {
+            stringBuilder.append(iterator.next());
+        }
+
+        assertEquals("AliceBobCharlie", stringBuilder.toString());
+    }
+
+    @Test
+    public void givenCollectionWithElements_whenUsingForLoop_thenAllElementsAreIteratedReverseOrder() {
+        List<String> names = Arrays.asList("Alice", "Bob", "Charlie");
+        StringBuilder stringBuilder = new StringBuilder();
+
+        for (int i = names.size() - 1; i >= 0; i--) {
+            stringBuilder.append(names.get(i));
+        }
+
+        assertEquals("CharlieBobAlice", stringBuilder.toString());
+    }
+
+    @Test
+    public void givenCollectionWithElements_whenUsingListIterator_thenAllElementsAreIteratedInReverseOrder() {
+        List<String> names = Arrays.asList("Alice", "Bob", "Charlie");
+        StringBuilder stringBuilder = new StringBuilder();
+
+        ListIterator<String> listIterator = names.listIterator(names.size());
+        while (listIterator.hasPrevious()) {
+            stringBuilder.append(listIterator.previous());
+        }
+
+        assertEquals("CharlieBobAlice", stringBuilder.toString());
+    }
+
+    @Test
+    public void givenCollectionWithElements_whenRemovingElementDuringForLoopIteration_thenConcurrentModificationExceptionIsThrown() {
+        List<String> names = new ArrayList<>(List.of("Alice", "Bob", "Charlie"));
+
+        assertThrows(ConcurrentModificationException.class, () -> {
+            for (String name : names) {
+                names.remove("Bob");
+            }
+        });
+    }
+
+    @Test
+    public void givenCollectionWithElements_whenRemovingElementUsingIterator_thenElementIsRemovedSafely() {
+        List<String> names = new ArrayList<>(Arrays.asList("Alice", "Bob", "Charlie"));
+        Iterator<String> iterator = names.iterator();
+
+        while (iterator.hasNext()) {
+            String name = iterator.next();
+            if (name.equals("Bob")) {
+                iterator.remove();
+            }
+        }
+        List<String> expected = Arrays.asList("Alice", "Charlie");
+        assertIterableEquals(expected, names);
+    }
+
+    @Test
+    public void givenCollectionWithElements_whenModifyingElementToLowerCaseDuringForLoopIteration_thenElementsAreModifiedToLowerCase() {
+        List<String> names = new ArrayList<>(List.of("Alice", "Bob", "Charlie"));
+
+        for (int i = 0; i < names.size(); i++) {
+            names.set(i, names.get(i).toLowerCase());
+        }
+
+        List<String> expected = Arrays.asList("alice","bob", "charlie");
+        assertIterableEquals(expected, names);
+    }
+}