test: added LinkedListStackTest

Author: alxkm

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

@@ -0,0 +1,72 @@
+package com.thealgorithms.datastructures.stacks;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.util.NoSuchElementException;
+
+public class LinkedListStackTest {
+
+    private LinkedListStack stack;
+
+    @BeforeEach
+    public void setUp() {
+        stack = new LinkedListStack();
+    }
+
+    @Test
+    public void testPushAndPeek() {
+        stack.push(1);
+        stack.push(2);
+        stack.push(3);
+
+        assertEquals(3, stack.peek());
+        assertEquals(3, stack.getSize());
+    }
+
+    @Test
+    public void testPop() {
+        stack.push(1);
+        stack.push(2);
+        stack.push(3);
+
+        assertEquals(3, stack.pop());
+        assertEquals(2, stack.pop());
+        assertEquals(1, stack.pop());
+        assertTrue(stack.isEmpty());
+    }
+
+    @Test
+    public void testPopEmptyStack() {
+        org.junit.jupiter.api.Assertions.assertThrows(NoSuchElementException.class, () -> stack.pop());
+    }
+
+    @Test
+    public void testPeekEmptyStack() {
+        org.junit.jupiter.api.Assertions.assertThrows(NoSuchElementException.class, () -> stack.peek());
+    }
+
+    @Test
+    public void testIsEmpty() {
+        assertTrue(stack.isEmpty());
+
+        stack.push(1);
+        assertFalse(stack.isEmpty());
+
+        stack.pop();
+        assertTrue(stack.isEmpty());
+    }
+
+    @Test
+    public void testToString() {
+        stack.push(1);
+        stack.push(2);
+        stack.push(3);
+
+        assertEquals("3->2->1", stack.toString());
+    }
+}