Well-behaved objects - Objects First with Java: A Practical Introduction Using BlueJ - page 243

Code 7.1
continued
The SalesItem class

if (cents <= 9) {
return "$" + dollars + ".0" + cents; // zero padding

}
else {
return "$" + dollars + "." + cents;

}

}

}

7.3.1 Using inspectors

When testing interactively, using object inspectors is often very helpful. In preparation for our
testing, create a SalesItem object on the object bench and open its inspector by selecting the
Inspect function from the object's menu. Select the comments field and open its inspector as
well (Figure 7.1). Check that the list has been created (is not null) and is initially of size 0.
Check also that the size grows as you add comments. Leave the comment-list inspector open to
assist with subsequent tests.

Figure 7.1
Inspector for the
comments list

An essential component of testing classes that use data structures is checking that they behave
properly both when the data structures are empty and—if appropriate—when they are full.
Testing for full data structures only applies to those that have a fixed limit, such as arrays. In
our case, where we use an ArrayList , testing for the list being full does not apply, because
the list expands as needed. However, making tests with an empty list is important, as this is a
special case that needs special treatment.

A first test that can be performed on SalesItem is to call its showInfo method before any comments
have been added. This should correctly show the item's description and price, and no comments.

A key feature of good testing is to ensure that boundaries are checked, because these are often
the points at which things go wrong. The boundaries associated with the SalesItem class are,
for example, the empty comment list. Boundaries set for the Comment class include the restric-
tion of the rating to the range 1 to 5. Ratings at the top and bottom of this range are boundary