We will start with testing the InvoiceItem class.

1. Add a field that we will test against:

   private InvoiceItem item;

2. Initialise the field in the setUp method:

   item = new InvoiceItem();
   item.setProductName("Polkadot Widget");
   item.setSalePrice(3.45);
   item.setQuantityPurchased(2.0);

   The setUp code is a little more complicated since we need to provide values for the initial state of the object.

3. Add test code to the testGetItemTotal method:

   Double result = item.getItemTotal();
   assertThat(result, is(6.90));

4. Fix the imports using <

   Fix Imports">>.

5. Run the test. It should pass.

6. Validate the test by breaking the getItemTotal method in the InvoiceItem class and run the test again. You can change the * operator to something else. The test should now fail.

7. Fix the method again so that the test passes.