refactor: StackArray (#5349)

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

@@ -0,0 +1,121 @@
+package com.thealgorithms.datastructures.stacks;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+class StackArrayTest {
+
+    private Stack<Integer> stack;
+
+    @BeforeEach
+    void setUp() {
+        stack = new StackArray<>(5); // Initialize a stack with capacity of 5
+    }
+
+    @Test
+    void testPushAndPop() {
+        stack.push(1);
+        stack.push(2);
+        stack.push(3);
+        stack.push(4);
+        stack.push(5);
+
+        Assertions.assertEquals(5, stack.pop()); // Stack follows LIFO, so 5 should be popped first
+        Assertions.assertEquals(4, stack.pop()); // Next, 4 should be popped
+        Assertions.assertEquals(3, stack.pop()); // Followed by 3
+        Assertions.assertEquals(2, stack.pop()); // Then 2
+        Assertions.assertEquals(1, stack.pop()); // Finally 1
+    }
+
+    @Test
+    void testPeek() {
+        stack.push(10);
+        stack.push(20);
+        stack.push(30);
+
+        Assertions.assertEquals(30, stack.peek()); // Peek should return 30, the top of the stack
+        Assertions.assertEquals(3, stack.size()); // Size should remain 3 after peek
+
+        stack.pop();
+        Assertions.assertEquals(20, stack.peek()); // After popping, peek should return 20
+    }
+
+    @Test
+    void testIsEmpty() {
+        Assertions.assertTrue(stack.isEmpty()); // Initially, the stack should be empty
+        stack.push(42);
+        Assertions.assertFalse(stack.isEmpty()); // After pushing an element, the stack should not be empty
+        stack.pop();
+        Assertions.assertTrue(stack.isEmpty()); // After popping the only element, the stack should be empty again
+    }
+
+    @Test
+    void testResizeOnPush() {
+        StackArray<Integer> smallStack = new StackArray<>(2); // Start with a small stack size
+        smallStack.push(1);
+        smallStack.push(2);
+        Assertions.assertTrue(smallStack.isFull()); // Initially, the stack should be full
+
+        smallStack.push(3); // This push should trigger a resize
+        Assertions.assertFalse(smallStack.isFull()); // The stack should no longer be full after resize
+        Assertions.assertEquals(3, smallStack.size()); // Size should be 3 after pushing 3 elements
+
+        Assertions.assertEquals(3, smallStack.pop()); // LIFO behavior check
+        Assertions.assertEquals(2, smallStack.pop());
+        Assertions.assertEquals(1, smallStack.pop());
+    }
+
+    @Test
+    void testResizeOnPop() {
+        StackArray<Integer> stack = new StackArray<>(4);
+        stack.push(1);
+        stack.push(2);
+        stack.push(3);
+        stack.push(4);
+
+        stack.pop(); // Removing elements should trigger a resize when less than 1/4 of the stack is used
+        stack.pop();
+        stack.pop();
+        Assertions.assertEquals(1, stack.size()); // After popping, only one element should remain
+
+        stack.pop();
+        Assertions.assertTrue(stack.isEmpty()); // The stack should be empty now
+    }
+
+    @Test
+    void testMakeEmpty() {
+        stack.push(1);
+        stack.push(2);
+        stack.push(3);
+        stack.makeEmpty();
+
+        Assertions.assertTrue(stack.isEmpty()); // The stack should be empty after calling makeEmpty
+        Assertions.assertThrows(IllegalStateException.class, stack::pop); // Popping from empty stack should throw exception
+    }
+
+    @Test
+    void testPopEmptyStackThrowsException() {
+        Assertions.assertThrows(IllegalStateException.class, stack::pop); // Popping from an empty stack should throw an exception
+    }
+
+    @Test
+    void testPeekEmptyStackThrowsException() {
+        Assertions.assertThrows(IllegalStateException.class, stack::peek); // Peeking into an empty stack should throw an exception
+    }
+
+    @Test
+    void testConstructorWithInvalidSizeThrowsException() {
+        Assertions.assertThrows(IllegalArgumentException.class, () -> new StackArray<>(0)); // Size 0 is invalid
+        Assertions.assertThrows(IllegalArgumentException.class, () -> new StackArray<>(-5)); // Negative size is invalid
+    }
+
+    @Test
+    void testDefaultConstructor() {
+        StackArray<Integer> defaultStack = new StackArray<>(); // Using default constructor
+        Assertions.assertEquals(0, defaultStack.size()); // Initially, size should be 0
+
+        defaultStack.push(1);
+        Assertions.assertEquals(1, defaultStack.size()); // After pushing, size should be 1
+    }
+}