XSLT Cookbook

Structuring Unit Tests

Problem

You want to structure tests to simplify testing.

Solution

Notice how Recipe 13.4 embedded test data in the test stylesheets. Each test element contains a test num attribute and the correct result in the form of an ans attribute. The test driver then extracts these test elements from the stylesheet, executes the test, and compares the expected answer against the actual answer. The most important aspect of the test driver is that it produces no output when the test succeeds.

Discussion

Some of the best advice on automating testing is in Brian W. Kernighan’s and Rob Pike’s The Practice of Programming (Addison Wesley, 1999). The authors state that test programs should produce output only when tests fail. Why? Who wants to wade through pages of test output to look for cases where the test fail? If you expect test code to produce no output, you will quickly notice failures when there is output. Of course, you should test your test code to make sure it actually executes before relying on this testing technique.

The method that stores the answer as an attribute in the test element works for simple tests that produce a primitive result. However, some templates produce node sets. In this case, you might need to store the correct answer as child elements in the tests. You can then use the value set operations of Recipe 7.2 to compare results. However, sometimes you can test node-set producing templates more simply. Consider the test driver for the math:lowest ...