Pragmatic Unit Testing in Java with JUnit, 3rd Edition

Increment 1: Deferring Complexity

For your first requirements batch, you’re tasked with delivering very simple rudiments of a portfolio.

You’ll be able to make purchases for the portfolio. For now, a purchase involves a stock symbol, such as SONO (Sonos) or AAPL (Apple), and a number of shares purchased for that symbol.

But your solution won’t need to track the actual symbols or shares of each. Madhu tells you that all it needs to answer are the following two things:

• Whether or not it is empty. A portfolio is empty if no purchases have been made and not empty otherwise.

• How many unique symbols have been purchased—the portfolio’s size. If you purchase AAPL once, you have one unique symbol. If you purchase AAPL a second time, you still have only ...