Interesting Talk: "In Search of Doors"

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• In Search of Doors

The Beverages Prices Refactoring kata: a kata to practice refactoring away from an awful application of inheritance.

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 coffe 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)));
	}
	}

view raw BeveragesPricingTest.java hosted with ❤ by GitHub

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.

Books I read (January - March 2019)

January
- Timeless Laws of Software Development, Jerry Fitzpatrick
- Writing to Learn, William Zinsser
- The End of the Affair, Graham Greene
- Beyond Legacy Code: Nine Practices to Extend the Life (and Value) of Your Software, David Scott Bernstein

February
- Refactoring Workbook, William C. Wake
- Binti, Nnedi Okorafor

March
- Home, Nnedi Okorafor
- The Night Masquerade, Nnedi Okorafor
- Developer Hegemony, Erik Dietrich
- The Ministry of Utmost Happiness, Arundhati Roy