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Software Testing-ISTQB ISEB Foundation Guide
There are very many ways to design test cases. Some are general, others are very specific. Some are very simple to implement, others are difficult and complex to implement. The many excellent books published on software testing techniques every year testify to the rate of development of new and interesting approaches to the challenges that confront the professional software tester.
There is, however, a collection of test case design techniques that has come to be recognized as the most important ones for a tester to learn to apply, and these have been selected as the representatives of test case design for the Foundation Certificate, and hence for this book.
The test case design techniques we will look at are grouped into three categories:
- Those based on deriving test cases directly from a specification or a model of a system or proposed system, known as specification-based or black-box techniques. So black-box techniques are based on an analysis of the test basis documentation, including both functional and non-functional aspects. They do not use any information regarding the internal structure of the component or system under test.
- Those based on deriving test cases directly from the structure of a component or system, known as structure-based, structural or white-box techniques. We will concentrate on tests based on the code written to implement a component or system, but other aspects of structure, such as a menu structure, can be tested in a similar way.
- Those based on deriving test cases from the tester's experience of similar systems and general experience of testing, known as experience-based techniques.
The category now known as specification-based was originally called ‘black-box’ because the techniques in it take a view of the system that does not need to know what is going on ‘inside the box’. Those of us born in the first half of the 20th century will recognize ‘black box’ as the name of anything technical that you can use but about which you know nothing or next to nothing. ‘Specification-based’ is a more descriptive title for those who may not find the ‘black-box’ image helpful. The natural alternative to ‘black box’ is ‘white box’ and so ‘white box’ techniques are those that are based on internal structure rather than external function.
Experience-based testing was not really treated as ‘proper’ testing in testing prehistory, so it was given a disdainful name such as ‘ad hoc’; the implication that this was not a systematic approach was enough to exclude it from many discussions about testing. Both the intellectual climate and the sophistication of experience-based techniques have moved on from those early days. It is worth bearing in mind that many systems are still tested in an experience-based way, partly because the systems are not specified in enough detail or in a sufficiently structured way to enable other categories of technique to be applied, or because neither the development team nor the testing team have been trained in the use of specification-based or structure-based techniques.
Before we look at these categories in detail, think for a moment about what we are trying to achieve. We want to try to check that a system does everything that its specification says it should do and nothing else. In practice the ‘nothing else’ is the hardest part and generates the most tests; that is because there are far more ways of getting anything wrong than there are ways of getting it right. Even if we just concentrate on testing that the system does what it is supposed to do, we will still generate a very large number of tests. This will be expensive and time consuming, which means it probably will not happen, so we need to ensure that our testing is as efficient as possible. As you will see, the best techniques do this by creating the smallest set of tests that will achieve a given objective, and they do that by taking advantage of certain things we have learned about testing; for example, that defects tend to cluster in interesting ways.
You may follow the complete series of Test Design Techniques articles here:
Test Development Process
The Idea of Test Coverage
Categories of Design Techniques
Specification Black Box Techniques
Structure based Whitebox techniques
Experience based Testing
Choosing Test Techniques
To see all articles of ISTQB-ISEB Foundation guide, see here:
Software Testing-ISTQB ISEB Foundation Guide
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