ShoppingCartTest.java

import static org.junit.Assert.*;

import java.util.ArrayList;
import java.util.List;

import org.junit.Test;

public class ShoppingCartTest {

	private static final int PRICE = 2;
	private static final int QUANTITY = 3;

	@Test
	public void addingItemChangesBasketTotal() {
		
		List<Object[]> basket = new ArrayList<>();
		
		String productCode = "P111";
		String productDescription = "Widget (Large)";
		double price = 10.0;
		int quantity = 10;
		
		addItem(basket, productCode, productDescription, price, quantity);
		
		double total = basket.stream()
				.mapToDouble(i -> (double)i[PRICE] * (int)i[QUANTITY])
				.sum();
		
		assertEquals(100.0, total , 0.0);
	}

	private void addItem(List<Object[]> basket, 
			String productCode, 
			String productDescription, 
			double price,
			int quantity) {
		
		Object[] item = new Object[] {
				productCode ,
				productDescription ,
				price ,
				quantity
		};
		
		basket.add(item);
	}

}