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3.3 Calculating Credit

Here's the business rule for our second example of using a ColumnFixture table to test calculations.

Credit is allowed, up to an amount of $1,000, for a customer who has been trading with us for more than 12 months, has paid reliably over that period, and has a balance owing of less than $6,000.

Again, we use a table to define whether credit will be extended, based on the values of the various given characteristics of our customers. A small set of tests for this business rule is shown in Figure 3.3.

Table 3.3. Fit Table for Testing Credit

CalculateCredit

months

reliable

balance

allow credit()

credit limit()

14

true

5000.00

true

1000.00

0

true

0.00

false

0.00

24

false

0.00

false

0.00

18

true

6000.00

false

0.00

12

true

5500.00

true

1000.00

The first row of the table names CalculateCredit, the fixture, which determines how the examples in the table are to be tested automatically against the system under test. In this book, we follow a convention that fixtures that test calculations have Calculate in their name.

The second (header) row of this table, as usual, labels the given and calculated value columns for testing creditworthiness. Two columns have calculated values: allow credit() and credit limit() . The given value of reliable and the calculated value of allow credit() will be either true or false. As is usual with ColumnFixture tables, the test rows are independent of one another.

In Figure 3.3, the four cell values in italics indicate that credit is refused. Test writers can format Fit tables to better organize them, as we'll see later, and format cells values of special interest to highlight them.

Fit reports the results as shown in Figure 3.4 (see also Plate 2). In each test row of the report, the two cells for the calculated results that are expected are marked. The tests in the first four rows are right and are marked in green. The last row of the table fails, with two cells marked wrong, in red.

03fig04.jpg

Figure 3.4 Fit Report for TestCredit

In general, a test can fail for several reasons. For example, in the report in Figure 3.4, the failing test itself could be incorrect, or the business rule may be stated incorrectly for the case of exactly 12 months.

Questions & Answers

  1. What if we want to use yes and no instead of true and false?

    They can be used instead in FitNesse (Chapter 8), where yes, y, 1, and + can also be used for true. Anything else is false.

  2. What if a given number is negative, which is not valid in the application?

    We take up this issue in Chapter 9.

  3. What's a fixture?

    A fixture is the "glue" that connects the tests in a Fit table to your application.

    From a programmer's point of view, a fixture names the software that is responsible for running the tests in the table against the system under test. Different fixtures may do different sorts of tests. Part III covers this in detail.

  4. Will a whole test sequence be included in one table? Some of our tests go on for many pages.

    No, not necessarily. We'll see in Chapter 6 that a test sequence may consist of many tables of varying types.

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