refactor: StackArrayList (#5356)

src/test/java/com/thealgorithms/datastructures/stacks/StackArrayListTest.java

@@ -0,0 +1,76 @@
+package com.thealgorithms.datastructures.stacks;
+
+import java.util.EmptyStackException;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+class StackArrayListTest {
+
+    private StackArrayList<Integer> stack;
+
+    @BeforeEach
+    void setUp() {
+        stack = new StackArrayList<>();
+    }
+
+    @Test
+    void testPushAndPop() {
+        stack.push(1);
+        stack.push(2);
+        stack.push(3);
+
+        Assertions.assertEquals(3, stack.pop());
+        Assertions.assertEquals(2, stack.pop());
+        Assertions.assertEquals(1, stack.pop());
+    }
+
+    @Test
+    void testPeek() {
+        stack.push(10);
+        stack.push(20);
+
+        Assertions.assertEquals(20, stack.peek());
+        stack.pop(); // Remove 20
+        Assertions.assertEquals(10, stack.peek());
+    }
+
+    @Test
+    void testIsEmpty() {
+        Assertions.assertTrue(stack.isEmpty());
+        stack.push(1);
+        Assertions.assertFalse(stack.isEmpty());
+        stack.pop();
+        Assertions.assertTrue(stack.isEmpty());
+    }
+
+    @Test
+    void testMakeEmpty() {
+        stack.push(1);
+        stack.push(2);
+        stack.push(3);
+        stack.makeEmpty();
+        Assertions.assertTrue(stack.isEmpty());
+        Assertions.assertEquals(0, stack.size());
+    }
+
+    @Test
+    void testSize() {
+        Assertions.assertEquals(0, stack.size());
+        stack.push(1);
+        stack.push(2);
+        Assertions.assertEquals(2, stack.size());
+        stack.pop();
+        Assertions.assertEquals(1, stack.size());
+    }
+
+    @Test
+    void testPopEmptyStackThrowsException() {
+        Assertions.assertThrows(EmptyStackException.class, stack::pop);
+    }
+
+    @Test
+    void testPeekEmptyStackThrowsException() {
+        Assertions.assertThrows(EmptyStackException.class, stack::peek);
+    }
+}