Abstract and concrete test cases

A dealership can give its salespeople the option of discounts to apply to the price of a vehicle. For prices below $15,000 there is no discount. For prices up to $20,000, a discount of 5% is appropriate. If the price is below $25,000, a 7% discount is possible. If the price is above $25,000, a discount of 8.5% is to be applied.

The above text enables us to derive the following relationships between price and discount:

Price < 15,000	Discount = 0%
15.000 ≤ Price ≤ 20,000	Discount = 5%
20.000 < Price < 25,000	Discount = 7%
Price ≥ 25,000	Discount = 8.5%

The text itself obviously offers potential for interpretation¹³. In other words, the text can be misunderstood, whereas the mathematical formulae derived from it are unambiguous.

Based on the formulae, we can define the following test cases (see table 2-2):

Table 2-2Abstract test cases

In order to execute these tests, the abstract cases have to be converted to concrete cases—i.e., we have to apply specific input values (see table 2-3). Exceptional conditions and boundary cases are not covered here.

Table 2-3Concrete test cases

The values shown here serve only to illustrate the difference between abstract and concrete test cases. We didn’t use a specific test technique to design these tests, and the cases shown aren’t meant to test the discount component exhaustively. For example, there is no test case that covers false input (such as a negative price). You will find more detail on the systematic creation of test cases using a specific test technique.

In addition to specifying abstract and concrete test cases, test design also includes prioritizing your test cases and providing appropriate testing infrastructure:

Priorities and traceability

• Test analysis has already prioritized the test conditions. These same priorities can be used and fine-tuned for your test cases (or sets of test cases). This way, you can assign different priorities to the individual tests within a set that are designed to verify a single test condition. High-priority tests are executed first.The same principle applies to the traceability of test conditions, which can be broken down to cover individual test cases or sets of cases.

Testing infrastructure and environment

• The required testing infrastructure has to be evaluated and implemented. Test infrastructure consists of all the organizational elements required for testing. These include the test environment, testing tools, and appropriately equipped workstations. A test environment is required in order to run the test object on a computer and verify the specified test cases (see below). This environment comprises hardware, any necessary simulation equipment and software tools, and other supporting materials. In order to avoid delays while testing, the test infrastructure should be up and running (and tested) before testing begins.

Following on from the test analysis, the test design stage can reveal further defects in the test basis. Likewise, test conditions that were defined at the analysis stage can be fine-tuned at the design stage.