DequeTest.java

import org.junit.Test;

import java.util.Iterator;
import java.util.NoSuchElementException;

import static junit.framework.TestCase.assertEquals;
import static junit.framework.TestCase.assertFalse;
import static junit.framework.TestCase.assertNotNull;
import static junit.framework.TestCase.assertTrue;

public class DequeTest {
    private final Deque<String> deque = new Deque<>();

    @Test
    public void isEmpty_initiallyTrue() {
        // Assert
        assertTrue(deque.isEmpty());
    }

    @Test
    public void isEmpty_afterAddingFirst_false() {
        // Arrange
        deque.addFirst("Hello");

        // Act
        assertFalse(deque.isEmpty());
    }

    @Test
    public void isEmpty_afterAddingLast_false() {
        // Arrange
        deque.addLast("!");

        // Act
        assertFalse(deque.isEmpty());
    }

    @Test
    public void removeFirst_oneElement() {
        // Arrange
        deque.addFirst("Hello");

        // Act
        String item = deque.removeFirst();

        // Assert
        assertEquals("Hello", item);
    }

    @Test
    public void removeFirst_multipleElements() {
        // Arrange
        deque.addFirst(" ");
        deque.addLast("World");
        deque.addFirst(",");
        deque.addLast("!");
        deque.addFirst("Hello");
        String result = "";

        // Act
        result += deque.removeFirst() +
                deque.removeFirst() +
                deque.removeFirst() +
                deque.removeFirst() +
                deque.removeFirst();

        // Assert
        assertEquals("Hello, World!", result);
    }

    @Test
    public void removeFirst_throwsOnEmpty() {
        // Arrange
        NoSuchElementException exception = null;

        // Act
        try {
            deque.removeFirst();
        } catch (NoSuchElementException e) {
            exception = e;
        }

        // Assert
        assertNotNull(exception);
    }

    @Test
    public void removeLast_throwsOnEmpty() {
        // Arrange
        NoSuchElementException exception = null;

        // Act
        try {
            deque.removeLast();
        } catch (NoSuchElementException e) {
            exception = e;
        }

        // Assert
        assertNotNull(exception);
    }

    @Test
    public void removeLast_afterCallingAddFirst_shouldRemoveFirstElement() {
        // Arrange
        deque.addFirst("One");

        // Act
        String last = deque.removeLast();

        // Assert
        assertEquals(last, "One");
    }



    @Test
    public void addFirst_ThrowsOnNull() {
        // Arrange
        IllegalArgumentException exception = null;

        // Act
        try {
            deque.addFirst(null);
        } catch (IllegalArgumentException e) {
            exception = e;
        }

        // Assert
        assertNotNull(exception);
    }

    @Test
    public void addLast_ThrowsOnNull() {
        // Arrange
        IllegalArgumentException exception = null;

        // Act
        try {
            deque.addLast(null);
        } catch (IllegalArgumentException e) {
            exception = e;
        }

        // Assert
        assertNotNull(exception);
    }

    @Test
    public void forEach() {
        // Arrange
        deque.addFirst(" ");
        deque.addLast("World");
        deque.addFirst(",");
        deque.addLast("!");
        deque.addFirst("Hello");
        String result = "";

        // Act
        for (String item:
             deque) {
            result += item;
        }

        // Assert
        assertEquals("Hello, World!", result);
    }

    @Test
    public void iteratorHasNext_afterAddingFirstAndRemovingLast_ShouldBeFalse() {
        // Arrange
        deque.addFirst("Hello");
        deque.removeLast();
        Iterator<String> iterator = deque.iterator();

        // Act
        boolean hasNext = iterator.hasNext();

        // Assert
        assertFalse(hasNext);
    }

    @Test
    public void iteratorHasNext_afterAddingLastndRemovingFirst_ShouldBeFalse() {
        // Arrange
        deque.addLast("Hello");
        deque.removeFirst();
        Iterator<String> iterator = deque.iterator();

        // Act
        boolean hasNext = iterator.hasNext();

        // Assert
        assertFalse(hasNext);
    }

    @Test
    public void iterator_afterRemovingOneItem_shouldNotHaveTheRemovedItem() {
        deque.addLast("one");
        deque.addLast("two");

        String item = deque.removeLast();

        int count = 0;
        for (String word:
             deque) {
            count++;
        }
        assertEquals(1, count);
    }

    @Test
    public void iterator_whenExhausted_throwsNoSuchElementException() {
        // Arrange
        Iterator<String> iterator = deque.iterator();
        NoSuchElementException exception = null;

        // Act
        try {
            iterator.next();
        } catch (NoSuchElementException e) {
            exception = e;
        }

        // Assert
        assertNotNull(exception);
    }
}