Rectangle Code

Rectangle.java

public class Rectangle {
    private final int width;
    private final int height;

    public Rectangle(int width, int height) {
        this.width = width;
        this.height = height;
    }

    public int perimeter() {
        return width * 2 + height * 2;
    }

    public int area() {
        return width * height;
    }
}

RectangleTest.java

import org.junit.Test;

import static junit.framework.Assert.assertEquals;

public class RectangleTest {

    @Test
    public void should_have_a_perimeter() {

        assertEquals(20, new Rectangle(5, 5).perimeter());

        assertEquals(18, new Rectangle(4, 5).perimeter());

    }

    @Test
    public void should_have_an_area() {

        assertEquals(1, new Rectangle(1, 1).area());

        assertEquals(20, new Rectangle(4, 5).area());

    }

}