The Beverages Prices Refactoring kata

I created the Beverages Prices Refactoring kata for the Deliberate Practice Program I'm running at Lifull Connect offices in Barcelona (previously Trovit). Its goal is to practice refactoring away from a bad usage of inheritance.

The code computes the price of the different beverages that are sold in a coffee house. There are some supplements that can be added to those beverages. Each supplement increases the price a bit. Not all combinations of drinks and supplements are possible.

Just having a quick look at the tests of the initial code would give you an idea of the kind of problems it might have:

package unit_tests;

import beverages.*;
import org.junit.Test;

import static org.hamcrest.CoreMatchers.is;
import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.Matchers.closeTo;

public class BeveragesPricingTest {
  private static final double PRECISION = 0.001;

  @Test
  public void computes_coffee_price() {
    Beverage coffee = new Coffee();
    assertThat(coffee.price(), is(closeTo(1.20, PRECISION)));
  }

  @Test
  public void computes_tea_price() {
    Beverage tea = new Tea();
    assertThat(tea.price(), is(closeTo(1.50, PRECISION)));
  }

  @Test
  public void computes_hot_chocolate_price() {
    Beverage hotChocolate = new HotChocolate();
    assertThat(hotChocolate.price(), is(closeTo(1.45, PRECISION)));
  }

  @Test
  public void computes_tea_with_milk_price() {
    Tea teaWithMilk = new TeaWithMilk();
    assertThat(teaWithMilk.price(), is(closeTo(1.60, PRECISION)));
  }

  @Test
  public void computes_coffee_with_milk_price() {
    Coffee coffeeWithMilk = new CoffeeWithMilk();
    assertThat(coffeeWithMilk.price(), is(closeTo(1.30, PRECISION)));
  }

  @Test
  public void computes_coffee_with_milk_and_cream_price() {
    Coffee coffeeWithMilkAndCream = new CoffeeWithMilkAndCream();
    assertThat(coffeeWithMilkAndCream.price(), is(closeTo(1.45, PRECISION)));
  }

  @Test
  public void computes_hot_chocolate_with_cream_price() {
    HotChocolateWithCream hotChocolateWithCream = new HotChocolateWithCream();
    assertThat(hotChocolateWithCream.price(),  is(closeTo(1.60, PRECISION)));
  }
}

If that's not enough have a look at its inheritance hierarchy:

To make things worse, we are asked to add an optional cinnamon supplement that costs 0.05€
to all our existing catalog of beverages. We think we should refactor this code a bit before introducing the new feature.

We hope you have fun practicing refactoring with this kata.