Pragmatic Unit Testing in Java with JUnit, 3rd Edition

Increment 4: Introducing a Test Double

For the final increment, Madhu tells you that you’ll need to capture and save a timestamp for each purchase or sale. He indicates that later requirements will need this information. These are the current requirements:

• Provide details about the last transaction (purchase or sale) made, including the timestamp.

• Produce a list of all transactions, ordered reverse-chronologically.

You choose to start with the requirement for the last transaction. Before you forget, you drop a zero-based test in place:

utj3-tdd/31/src/test/java/app/APortfolio.java

@Test
void returnsNullWhenNoPreviousTransactionMade() {
    assertNull(portfolio.lastTransaction());
}

The next test, a one-based test for the last transaction, ...