documentation/src/test/java/example/TestingAStackDemo.java

/*
 * Copyright 2015-2022 the original author or authors.
 *
 * All rights reserved. This program and the accompanying materials are
 * made available under the terms of the Eclipse Public License v2.0 which
 * accompanies this distribution and is available at
 *
 * https://www.eclipse.org/legal/epl-v20.html
 */

package example;

// tag::user_guide[]
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 java.util.EmptyStackException;
import java.util.Stack;

import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.DisplayName;
import org.junit.jupiter.api.Nested;
import org.junit.jupiter.api.Test;

@DisplayName("A stack")
class TestingAStackDemo {

	Stack<Object> stack;

	@Test
	@DisplayName("is instantiated with new Stack()")
	void isInstantiatedWithNew() {
		new Stack<>();
	}

	@Nested
	@DisplayName("when new")
	class WhenNew {

		@BeforeEach
		void createNewStack() {
			stack = new Stack<>();
		}

		@Test
		@DisplayName("is empty")
		void isEmpty() {
			assertTrue(stack.isEmpty());
		}

		@Test
		@DisplayName("throws EmptyStackException when popped")
		void throwsExceptionWhenPopped() {
			assertThrows(EmptyStackException.class, stack::pop);
		}

		@Test
		@DisplayName("throws EmptyStackException when peeked")
		void throwsExceptionWhenPeeked() {
			assertThrows(EmptyStackException.class, stack::peek);
		}

		@Nested
		@DisplayName("after pushing an element")
		class AfterPushing {

			String anElement = "an element";

			@BeforeEach
			void pushAnElement() {
				stack.push(anElement);
			}

			@Test
			@DisplayName("it is no longer empty")
			void isNotEmpty() {
				assertFalse(stack.isEmpty());
			}

			@Test
			@DisplayName("returns the element when popped and is empty")
			void returnElementWhenPopped() {
				assertEquals(anElement, stack.pop());
				assertTrue(stack.isEmpty());
			}

			@Test
			@DisplayName("returns the element when peeked but remains not empty")
			void returnElementWhenPeeked() {
				assertEquals(anElement, stack.peek());
				assertFalse(stack.isEmpty());
			}
		}
	}
}
// end::user_guide[]