StackUsingLinkedListTest.java

package com.thealgorithms.stacks;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertFalse;
import static org.junit.jupiter.api.Assertions.assertThrows;
import static org.junit.jupiter.api.Assertions.assertTrue;

import org.junit.jupiter.api.Test;

/**
 * Test class for StackUsingLinkedList.
 *
 * This class contains unit tests to verify the correctness
 * of stack operations such as push, pop, peek, and isEmpty.
 *
 * Reference: https://www.geeksforgeeks.org/stack-using-linked-list/
 */
class StackUsingLinkedListTest {

    /**
     * Test push and pop operations
     */
    @Test
    void testPushAndPop() {
        StackUsingLinkedList stack = new StackUsingLinkedList();
        stack.push(10);
        stack.push(20);

        assertEquals(20, stack.pop());
        assertEquals(10, stack.pop());
    }

    /**
     * Test peek operation
     */
    @Test
    void testPeek() {
        StackUsingLinkedList stack = new StackUsingLinkedList();
        stack.push(5);

        assertEquals(5, stack.peek());
    }

    /**
     * Test isEmpty method
     */
    @Test
    void testIsEmpty() {
        StackUsingLinkedList stack = new StackUsingLinkedList();

        assertTrue(stack.isEmpty());
        stack.push(1);
        assertFalse(stack.isEmpty());
    }

    /**
     * Test pop on empty stack (edge case)
     */
    @Test
    void testPopOnEmptyStack() {
        StackUsingLinkedList stack = new StackUsingLinkedList();

        assertThrows(RuntimeException.class, stack::pop);
    }

    /**
     * Test peek on empty stack (edge case)
     */
    @Test
    void testPeekOnEmptyStack() {
        StackUsingLinkedList stack = new StackUsingLinkedList();

        assertThrows(RuntimeException.class, stack::peek);
    }
}